The Ice Cave is only occupied by two types of enemies. The first is the various spirits that dwell in the ice of the cave itself. They appear as black faces in the ice, and they spit fireballs in a straight line. They can be removed with a slash of the sword, or a thrown dagger. The second enemy is a living stalagmite, which rises from various platforms, travels forward in one direction, and then shrinks back down to the ground. Though you can hit them to make them retreat early, you can't actually defeat them, and they are better avoided altogether.
The Ice Cave is a large level, and you begin at the very top. If you know the level well enough, you can minimize the amount of backtracking you do by clearing the level from the top to the bottom. The map has been divided into two halves. In the top half, you will only find blue treasure chests, but the blue key is surprisingly easy to miss. If you happen to have the Boots of Force, that's not necessarily a problem, although two items in this stage can replace the Boots, and you'll lose them if you're unfamiliar with the contents of each chest.
The blue key is found by dropping down to the floor below the stage entrance, and walking to the left. You'll find a platform with a blue treasure chest (A) to the left. There is a ledge above and to the left of this chest that you can jump to. Keep climbing above this ledge and you will reach the platform which contains the blue key. Now you can drop back down to the chest and collect the diamonds it contains.
From the remaining blue chests, you can pick up a few useful items. Ignoring treasure chest B for the moment, if you make your way down the cave, you will reach chest D, which contains more diamonds. To the right of that is a platform where a blue potion continuously appears. Just below this blue potion is another chest (E) which contains a helpful tool, the Potion of Levitation. After collecting this, you can hold to levitate slightly off the ground before jumping and reaching higher platforms. Finally, to the right of the blue potion, and high above a series of ledges is chest C which contains the Cloak of Darkness. Collecting the blue potion makes the first ledge at the bottom of the climb easier to reach. The cloak will replace your Boots of Force. While it's somewhat useful for granting near invincibility, it's arguable that the Boots might be a better item to hang on to.
Collecting the Feather
Though it may not appear so, treasure chest B is actually a bit challenging to reach. The platform that leads to the small entrance on the right is situated in just such a way that Kuros can't get a foothold by jumping. Experts in the game have found a way to make the jump from the ledge, but it's considerably difficult to do. There is another way to make this jump successfully, but it requires patience, practice, and steady controls.
Make your way down to the platform with the blue potion (to the right of chest D). Jump over the potion and start from the right side. When you're ready, run to the left and pick up the potion. You will gain a boost in speed from the potion. As quickly as you can, jump back up the ledges until you can enter the open region to the right. From here, you must jump over the ledge with the red potion by using the smaller platforms above. If you land on the red potion, you will lose the benefit of speed and be unable to make the jump. Provided you have made it to the platform just before the opening without losing the effects of the blue potion, leap over to the right, and the added speed should help you clear the steep surface and land on the flat ledge with the diamond. From here, you can continue to the right and collect the contents of chest B.
Inside, you'll find the Feather of Feather Fall. With this helpful item, you can hold while you are falling to slow your descent, and guide Kuros through the air to destinations that you might otherwise fall to quickly to access.
The bottom half of the cave is all of the region below the last blue treasure chest E (which contained the Potion of Levitation). This half contains three treasure chests and a door, all of which are red. For them, you'll need the red key, and it happens to await you near the top of this portion of the cave. To reach it, you must jump to the right from the right platform above chest G. The pink potion nearby can help you reach the ledge that the key is found on, but it isn't actually necessary.
Once you have the key, you can open up the remaining chests in the main part of the cave. Chest F contains more diamonds, which will help you get that much closer to the 100 diamonds you need to exit the level. Chest G gives you another opportunity to collect the Shield of Protection. However, if you already acquired it from the first stage, then it will have another batch of diamonds. Finally, chest H situated above the exit from the stage contains the Boots of Lava Walking, which will replace the Boots of Force. If you're new to the game, it is highly recommended that you collect these boots before you proceed to the boss battle and the stage beyond. If you're a more experienced player, you can judge how effective you are at staying off the lava floor of the Lava Cave and decide if you should collect them.
The cave of diamonds
Finally, there is the red door at the very bottom of the cave, on the left side. If you have the red key, you can access this door and explore the small enclosure on the other side. In here, you will find plenty of diamonds, along with three chests, one blue and two pink. You probably already have the blue key, so if you open chest K, you will obtain the Dagger of Throwing if you failed to collect from the first stage. Otherwise it will be more diamonds. You won't be able to open the other two chests without the Boots of Force just yet.
If you explore the cavern thoroughly and climb to the top, you will find the pink key waiting for you to collect. You may be surprised, however, when you go to jump from the small platform below to the pink key. It just so happens that there is a secret stash of diamonds hidden in the space above the small platform. Jump up continuously to collect the diamonds until they stop appearing, and then jump up to collect the key.
Dropping back down, you can now open the chests with the key. Chest I contains more diamonds while chest J will hold another Potion of Levitation if you failed to collect the one from chest E in this stage earlier. If you already found the potion, then this chest will contain more diamonds as well. By now you should have an ample supply of diamonds, and be able to walk past the knight guarding the exit from the cave.
Boss: Giant Bat
Making your way from the exit in the lower right corner of the cave, you will find yourself in a long corridor. Along the ceiling of this corridor are a series of bats, first small, and then large. You might be tempted to stop and fight each one as they plunge down to attack you, but you're actually better off ignoring them and running all the way to the right. The fact is that the game only allows so many bats to pursue you, and once that limit is reached, subsequent bats will remain on the ceiling. By the time you reach the end of the corridor, below the biggest bat of all, several of the larger bats will have completely ignored you.
Cornered in the back of the cave, you must now turn around and defend yourself from the flurry of bats that have been chasing you. Take out as many as you can before the reach you, and destroy them while attempting to lose as little health as possible. Once the group of bats have been cleared, you just have two large bats to destroy before the Giant Bat will engage you. Move to the left trigger each bat one at a time and defeat them. Once they are cleared, the Giant Bat will drop down to attack.
The Giant Bat moves rather predictably in an effort to fly straight toward you. Because of this, it is easy to steer the bat by letting it follow you into one corner and then jumping over it and running to the opposite corner. As you make each run, attack it with a throwing dagger, and let the dagger fly around you a bit to score more damage against the bat. Continue the pattern of attacking, luring the bat to a corner, jumping over it and running to the opposite corner until the bat runs out of health and is defeated. At this time, a collection of souls will appear when the bat is defeated. Though weak, these souls can still harm you and defeat you before you clear the stage, so be ready to defend yourself and attack them as quickly as possible. Once the last soul is defeated, a pile of treasure will rise from the floor. Collect it, and you will run through the door and rescue Esmarelda for 10,000 bonus points before proceeding to the next stage.