Once you have the Grapple Beam you can go after the X-Ray Visor or the Plasma Beam next. Apparently the hint system can point you to either one at this point; perhaps it shows you the one closest to territory you've already explored. Regardless, we're going to cover the X-Ray Visor next because it's been reachable since you got the Power Bomb.
Great Tree Hall
Return to the Great Tree Hall and jump up to the ledge above the gate you opened earlier. There is a pillar with Spider Ball track spiraling around it. Make your way to the top and to the end of section of track that sticks out at the top. Drop to a lower side section and spiral up a branch pillar to the ledge above. Now go through the door here.
Life Grove Tunnel
Drop a Power Bomb to clear the boulder out of the path, then continue into a Morph Ball maze. This one has a half-pipe structure built in which closes into a loop. Start swinging around with the Boost Ball until you get enough momentum to carry you to the top of the loop. There's a weak spot there which will break open if you drop a bomb there, and if you drop through you'll have a Missile Expansion by the time you come out the bottom. Continue into the next room.
Drop off the ledge to find the X-Ray Visor. Like the Thermal Visor, it allows you to see objects that are invisible in normal light. But since it uses a different part of the spectrum you can see objects that are invisible in the Thermal Visor as well. Conversely, objects only visible in the Thermal Visor will usually still be invisible in X-Ray.
It appears at first glance that you're trapped in this little room, but if you switch to X-Ray you can see that there is more to it beyond the walls you can see. Drop a Power Bomb in the middle to break down most of the walls and reveal a much larger valley. (There is an endless stream of Seedlings that slowly crawls down the wall here, and they will nearly always drop Power Bomb ammo in case you're low.)
Now you can start finding a way out. Go left from the start to a large tree, then jump to the ledge next to it, and to another ledge with a Morph Ball sized groove in the wall. Follow the groove to a catwalk, then platform your way around the large tree to trigger an attack by Chozo Ghosts.
Fight these as usual, but you can use the X-Ray Visor to keep a lock on them making it somewhat easier. When the battle is over, a statue on the roof of the little room breaks revealing a hole for a Morph Ball.
Start following the route beginning at the large tree again, but this time there's nothing to stop you from reaching the end which is the where the hole appeared. Drop in to find yourself on the ledge where you came in. Before going back though, there is a Chozo Artifact you can get here, see the Chozo Artifacts page for details.
Expansions (Tallon Overworld)
Great Tree Hall (cont.)
When you get back to the Great Tree Hall, check the map to get a rough idea where the last door is. It appears to be behind the tree but there is no way to reach it. From now on, when something seems to be out of reach, switch to X-Ray and look for cloaked platforms since that will often be they way to reach it.
When you switch to X-Ray here you'll find a cloaked platform floating above the entrance to Transport Tunnel D. Platform your way to it, and now switch to normal vision and look down to see the rain splashing on the platform even though you can't see the platform itself. This is sort of a sequence break in that it allows you to locate the platform before getting the visor. It only works in Tallon Overworld because of the rain, and you probably won't be able to find the splashes unless you already know where to look.
Jump from the cloaked platform to a ledge behind the tree to find a door there.
Great Tree Chamber
A Missile Expansion is waiting for you in this little room. It's a pretty little room so take a moment to appreciate the effort someone put in to create it just for this one expansion.
There is another Missile Expansion in Tallon Overworld you can get now, but it's very close to another expansion that requires the Plasma Beam so we'll cover them together on the next page.
Expansions (Magmoor Caverns)
Go back to the Triclops Pit and you may notice that one of the pillars in the middle of the room gives off an expansion hum. Switch to X-Ray and look near the top to see that part of the pillar is transparent to X-Ray. The expansion is there but the problem is how to reach it. Again in X-Ray, look around the pillar to see a cloaked platform, and look near that for a second, and finally locate the third near the entrance from the Pit Tunnel.
Starting from the ledge near the third platform, start jumping from one to the other in reverse order until you're facing the pillar with the expansion. Fire a Missile to break the rock, then do a final jump to collect the Missile Expansion.
Expansions (Phazon Mines)
There's another expansion to get on the lower level of the Phazon Mines. You'll be passing through the room with the Plasma Beam to get there, so it may seem to be going out the the way, but it won't be any less out of the way after getting the Plasma Beam so you might as well get it now.
Phazon Processing Center
Get to the Phazon Processing Center; you may notice that the platform in Transport Access is gone and you now have to use the Grapple Beam to get through without wading through Phazon.
Get to a ledge about half way down the wall opposite the entrance from Transport Access. There is a hum coming from the wall and if you switch to X-Ray you can see a Missile Expansion inside it. Drop a Power Bomb to break open the wall and get the expansion.