Pokémon HeartGold and SoulSilver/Dark Cave

There isn't much you can do in the Dark Cave at first, so you might as well push on to Violet City. You will only have access to one room right now and it's pitch black. One of the most noticable things is that this is the first place in the game to get your hands on a, which isn't great on its own but with a little love and leveling, you can quickly get a very strong.

To get any further into the cave, you'll need to teach a Pokémon Flash to light up the cave for you to explore, and a Pokémon that knows Rock Smash, Strength and Surf to enable you to get past certain obstacles. You won't have either yet, so you should leave this cave for later on when you can make more headway in it.

Returning to Dark Cave
When you do eventually return to Dark Cave, there are a couple of items that are worth scooping up. The Black Glasses, given to you by a man close to the Blackthorn exit/entrance can power up all manner of dark-type moves such as Bite, Crunch, Dark Pulse and Feint Attack.

There are two TM's in here as well. TM54 (False Swipe) isn't too helpful at this late stage of the game - it's main use is for helping catch Pokémon by getting their health down to 1HP - but fortune favours the prepared, so scoop it up and leave it in the bag until you may need it. The other TM, TM13 (Snore) is more helpful. Although not as powerful as its counterpart, Sleep Talk, Snore allows you to use a damaging move whilst asleep and is ideally used in conjunction with Rest. Quite why you would use this TM instead of simply waking the Pokémon up with an item is anyone's guess, but everyone has their own play style.

Dark Cave leads to the following routes:
 * ../Route 45/ (to Blackthorn City)
 * ../Route 31/ (to Violet City)
 * ../Route 46/ (to New Bark Town).

Items

 * Potion
 * Dire Hit
 * Full Heal
 * Hyper Potion
 * Black Glasses
 * Revive
 * TM False Swipe

Pokemon

 * Zubat
 * Geodude
 * Dunsparce