Final Fantasy X/Mi'ihen Highroad
Mi'ihen Highroad is a long stretch of road leading between Luca and Djose Temple (technically the Temple of Yevon-Djose, but still).
 Traveling along the Highroad
Use the Save Sphere up here to save your game and heal up. Make sure you talk to as many people as possible whilst walking along the Highroad, because a lot of them have gifts for Yuna which you can put to good use. Make sure you keep chatting to the scholar guy in front of the statue too, since he has a lot of historical information that you might want to know.
The first battle you come across is predetermined. This introduces armoured enemies — only Kimahri and Auron have weapons with the Piercing auto-ability by default, so only they can inflict sensible damage on them. So, you should leave wolves and lizards to Tidus, aerial enemies to Wakka, elements and flans to Lulu, and armoured enemies to Auron (and Kimahri, to a lesser extent).
Keep walking along the Highroad. The large structure on the left hand side a short way along (which the scholar, Maechen, will talk to you briefly about) has an Ice Brand behind it if you didn't already pick one up. A little further along you'll be introduced to the Chocobo Knights (of which there are only three you ever meet — weird).
There are quite a few different enemies you will encounter on Mi'ihen Highroad compared to that of Besaid or Kilika Woods, and here's a brief explanation of them:
- Mi'ihen Fangs are wolves, so they're magic-resistant and nimble. Their attacks aren't especially powerful or status-heavy, but only Tidus and Wakka can reliably hit them.
- Dual Horns have nasty physical attacks, doing a lot of damage apiece. They aren't armoured or resistant to magic but they have quite a bit of health. You can Lancet these for Fire Breath, too. To defeat them, make sure you inflict darkness with Dark Attack and use Power Break with Auron to reduce its strength. After that just attack it normally.
- Floating Eyes are resistant to magic but won't use any — they have a weird stare attack which hits one person and might confuse them, and a weirder breathing wave attack that hits everyone for similar damage (no confusion, though). One hit from Wakka is enough to kill them, but they will dodge pretty much every other person's attacks.
- Raldos are the same monsters as the one you fought in the piercing weapons predetermined battle — don't bother hitting them with anyone except Auron or Kimahri. They have a ramming attack which can hurt a bit, but otherwise one hit from Auron will kill them.
- White Elements have the same basic properties as the Yellow Elements from Kilika Woods, except their native element is ice, this time. So, use Fire on them. As before, physical attacks do barely anything, and any other element magic is a bad idea (either low damage or absorption).
Anyway, towards the end of the first section of the Highroad, you'll encounter a side section with a lady standing in front of a ruin. Talk to her; she's Belgemine, and will help you train summon usage for related parts of the storyline. You also get a free summon heal before the battle, too.
 Fighting Belgemine's Ifrit
Because you're fighting Ifrit you can't summon your own Ifrit, so you can only use Valefor for this battle (quite a big drawback). Your opponent will use attack, Meteor Strike, attack, Meteor Strike in that order, then its overdrive Hellfire once that's full. The on-screen instructions will help you out as well — unless you're going to use Energy Ray, use Shield before Ifrit uses Meteor Strike on you. Don't use normal attacks or Sonic Wings on Ifrit, either, since Valefor's Blizzard will do more damage than either of them and Ifrit is immune to delay. Ultimately it will be no surprise if you don't win this battle — it's rather difficult considering you have no backup aeons and Valefor isn't really that good anyway. The best way to approach this battle is to charge both Yuna's and Valefor's Overdrive to full and attack Ifrit from there. You'll get something from it regardless of whether you win or not; a ring for Yuna which isn't especially useful anyway.
Keep heading along the road until you reach the next screen. The chest off to the top from the main road (past one of the elusive Chocobo Knights) contains a Remedy. You'll learn a little more about the perpetuity of Sin further along. If you're a mean and spiteful Tidus as opposed to a good and morally-enriched Tidus, you can kick the little kid's Blitzball away.
The next screen is another long section of road. There's nothing in the first side bit on the left, so keep going, remembering to talk to people for more goodies. One thing you will definitely want to get is a Level 1 Key Sphere from a guy walking around near the right hand side bit further up this section of Mi'ihen Highroad. In that side section there is also a chest containing 2000 Gil.
Further along you'll encounter a chocobo-pulled trailer, and Luzzu and Gatta in a nearby side section. Although they won't reveal much about their plan, a Yevon priestess of sorts, Shelinda, is arguing with a Crusader up ahead and she'll tell you a bit more. Make sure you pick up the 3 Eye Drops in the chest just before the path to the next section.
You'll be outside an Al Bhed inn/shop/travel agency of sorts. You'll enter it and rest. There's quite a long scene ahead of you with Tidus and Yuna. Afterwards, you'll meet Rin, the owner of these shops, and get an Al Bhed primer (Al Bhed Prime VIII). Something appears to be attacking the chocobos; time to help out.
 Boss Battle: Chocobo Eater
That's one ugly fiend, isn't it? The Chocobo Eater can be quite a tough customer if you're not careful. His attacks hurt — his normal one does about 450 damage, and Fist of Fury, which comes after "You're Next!" does 950! He also has a ramming attack that does a proportion of their current health to everyone, and pushes them backwards. This has a special significance, since you'll also be pushing it backwards too.
It has 10000 HP, so it won't go down quickly. Hit it with Dark Attack and Power Break to even the odds a little, then just attack it. It's armoured whilst upright, so both Tidus and Wakka will be doing less than 80 damage a hit. Auron and Kimahri will do more since their weapons are piercing. Bring out all the strong physical attackers when it falls over backwards, so you can push it back. Its bum isn't armoured, so you can do normal damage. Whilst it's on its back, the turns it takes will either be doing nothing, getting back on its feet, or casting Blizzard, which does about 100-200 damage to one person.
Summons aren't recommended simply because they're slow — you need to be quick in this fight and make sure you keep up the punishment, otherwise you'll go over the cliff. Your aim in this battle is either to kill it, or shove IT off the cliff instead, providing you push it back far enough. The reward you get from this battle depends on how you "win" it — killing the Chocobo Eater nets you experience and Gil, but knocking it off gets you 2 Level 1 Key Spheres. It's probably best to go with the easier method of killing it.
 Reaching Mushroom Rock
This part of the guide will cover the two paths that you can take from here to the entrance to Mushroom Rock Road.
 The Chocobo Path
You'll get to take this path if you either knocked the Chocobo Eater off the cliff, or killed it. Either way you can get a free Chocobo ride for the nice and simple path to Mushroom Rock Road. There are some goodies along the way that you might want to get, however, using the chocobo:
- In the second section of this path, there's a yellow chocobo feather on the outside of the right-hand turn. These are basically indicators of where your chocobo can jump, so press X when near it and you'll automatically ride your chocobo to an otherwise inaccessible place. Here you can get a chest on a rock sticking out of the rockface, containing a Heat Lance for Kimahri. Don't forget the Al Bhed Primer ix across from the yellow feather.
- When you reach the gate to Mushroom Rock Road, you can actually make a U-turn and ride your chocobo down the path you would have taken if the Chocobo Eater knocked you off. After a few narrow bits (around where the inaccessible section of path is on your mini-map) there's a somewhat hard-to-see chocobo feather on the ground to the left. You get two chests from this one — the first is a Thunder Blade for Auron and the second is a Scout for Wakka (similar to the one you got from Kilika Woods, except this one has Sensor and Lightningstrike as opposed to Sensor and Icestrike).
- A little further back down the lower path, there's a concealed fork in the road that you can spot on your mini-map. The chocobo feather here leads to an elusive Fortune Sphere, that you can use to activate Luck nodes (but don't use either this or the Luck Sphere you got from Luca yet — they're very important indeed towards the end of the game).
You can also get the other stuff from the lower road if you're on the chocobo, but that's outlined below.
 The Oldroad
You'll take this path if the Chocobo Eater shoved you off the cliff. The only major problems here are that it's a pain to get the chocobo treasures now (it'll also cost you 1000 Gil) and there are random battles all the way along to the entrance to Mushroom Rock Road.
First off, though, you can pick up the Mars Crest from the chest here. It's useless for the mean time although by picking it up now it will save you time later (although if you want to power up Auron more, you'll be coming back here anyway). The random battles are mostly similar to the ones you encountered on the main road. O'aka is rather handily along here if you want to buy anything or feel like lending him some more Gil. Either way, it's just another random-battle filled path (you'll meet Lucil along here as well).
 Mushroom Rock Gate
Either way, at the end of the paths you'll be confronted by quite a large gate accompanied by more trailers and some Chocobo Knights. The chest on the left-hand side of the screen here has 2 Hi-Potions. Save your game and then approach the gate and Luzzu and Gatta will greet you again. The trailer will move along. If you try and follow it through the Crusader guy standing on the edge will stop your passage. Finally you'll get an opportunity to be told what they're actually doing, although it's still not QUITE the full story, as you'll soon see. The guy standing on the left in the actual gate will take offers for donations — you'll get an item depending on how much you give him. Of course, you don't have to donate anything but it's pointless to give him 10,000 Gil. However, if you are feeling generous, you can give him gil - 100 gil gives you a Scout, 1,000 gil gives you an Ice Lance, and 10,000 gil gives you a Moon Ring.
If you try to leave Maester Seymour will show up. What the hell is he doing here? It doesn't matter though since he'll get you let through. That was kind of him. Go back and save your game if you didn't before, then keep walking along to enter Mushroom Rock Road!