Even in an underground cavern, the temperature is so cold that ground water has frozen over, forming slippery blocks of ice. In addition to the usual cave lurkers like Piranha Plants and Swoopers, you also have to contend with large amounts of Spike Tops. With flame resistant shells and harmful spikes, there's very few things that can defeat them!
Go into the starting warp pipe to enter the cave. As you proceed forward, you'll notice a huge rectangle of brick blocks, with several pockets that contain Spike Tops. A cousin of the recurring Buzzy Beetle enemy, they can't be taken out by stomping or by fireballs, attempting the former even causes you to get hurt! You can usually beat them by hitting the block they're standing on, but a Shell Dash, Star or Mega Mushroom will work just as fine if you happen to have the item. If you can break a path to the top of this formation, you can get a load of coins in the ceiling offscreen.
To the right, you'll come into more direct contact with the Spike Tops. One patrols the stone block you're standing on, while the other goes around the single question-mark block. Hit the block to defeat the Spike Top and get the power-up inside. The ice block to the right also contains a Spike Top. Jump from the block down to the ice slope. As can be expected, icy surfaces are slippery, so you will take a longer time to come to a stop. There's also multiple Swoopers that will swoop down at you from the ceiling.
After this, you will get to a small area with many pipes next to each other. The pipes all contain Piranha Plants, which the icy surface below can cause you to slide into. Learn to jump to come to a quick stop when you're on the ice. The leftmost block just before the series of pipes containa a 1-Up, which you have to dash past the pipes to collect. Only attempt to get this is you have a Blue Shell or Fire Flower, since you're likely to miss the 1-Up or get hit by a Piranha Plant without them. In the middle of the series of pipes, there is a Star Coin. Hit the blocks below it so you can hop up and collect it.
To the right is a sizable stretch of ice. The density of Spike Tops will be higher from now on, and there's quite a few on the lone blocks around here. Heading right, you should see a Star Coin between two blocks with a pair of Spike Tops circling around them. Use the spring below to reach it, holding either jump button as you land on the spring to get propelled the maximum distance. Go right a bit to pass the checkpoint, then take the spring with you left. Jump over the gap and place the spring below the yellow pipe. Use the spring to jump into the pipe.
Through the pipe, you will be taken to the surface, where there are many narrow icy platforms. As you approach the lone coin, it turns out to be a Moneybag. These creatures dispense coins every time you hit them with a stomp or a fireball, take 6 hits with either method to kill, and drop a 1-Up Mushroom upon defeat. Your objective is not to defeat the Moneybag, but to follow it across the ice platforms. At the end, there is the next Star Coin within jumping distance. Head down the pipe to the right to return to the cave, just slightly ahead of the location of the previous Star Coin.
After the pipe, you're given a choice of two routes. You can choose to wall jump up to the top of the block formation ahead, which has many Spike Tops but more coins, including a 10-coin block at the end of the path, or proceed straight forward along the bottom path, evading several Swoopers. You can ignore the top path if you're not concerned about getting coins. After this, you will jump across some more gaps,, on to some platforms with Spike Tops circling around them. Proceed with care so you don't run into any of the Spike Tops. After two pipes, you have to jump on to some more ice platforms with Spike Tops. Stay steady until you reach the exit pipe, which takes you up to the flagpole.
- This Star Coin is above some blocks in the section along the level that has many pipes filled with Piranha Plants. Break the blocks and jump to get it.
- It is best to attempt to get this coin after the third. Carry the spring below the third Star Coin left to a yellow pipe. Use the spring to jump into the warp pipe, then move to the right of the bonus area and jump up to get the Star Coin.
- Near the checkpoint, there is a spring below an easily visible Star Coin. Jump on the spring to be launched up to the coin. Watch out for the Spike Tops as you do.
The secret exit of this level is not particularly hard to get, but not very obvious either. As you go through the stage, keep a lookout for a brick block formation that includes four coins horizontally level above an extension of the formation, also preceded by a Swooper. From this makeshift landmark, go right and get on the ice block. There is a pipe with a Piranha Plant in it at the ceiling above the ice block. Simply jump into the warp pipe when the Piranha Plant is not present to be taken to the red flagpole.
This secret exit opens up a path south into an overworld warp pipe. The warp pipe lets you skip the tower, instead going right to World 5-3.