This is the easiest cave in the game. It contains 3 treasures and 11 Snow Bulborbs. Try to bring as many Red Pikmin as you can get.
Defeat the Snow Bulborbs. They shouldn't be too hard, so attack with any method you want. Remember, throwing Pikmin on their backs kills them instantly, but swarms of 70+ Pikmin can do the same thing. Their bodies are worth a few Pokos. Also, get the Orange and Bottle Cap. Then go to Sub-level 2.
Defeat the Snow Bulborbs. There are 7 of them, but still not much of a threat. You will notice half of a globe, lying on the floor. You can't lift it with 100 Pikmin. Hmm, here's a puzzler... you need 101 Pikmin to lift it, but you can only have 100 on the field... how do you get this thing? Purple Pikmin! You'll find Violet Candypop Buds near the exit. Throw in 10 Red Pikmin. The Violet Candypop will turn them into Purple Pikmin. Pluck the Purples and grab the treasure. Purples can lift ten times as much as other Pikmin. Also, they can stun enemies when thrown. Beware their slowness, however. Grab the half globe. It will open up Awakening Wood. Leave through the geyser. Make sure to pluck any purple Pikmin. If they're left in the ground, they'll die.
You will need all five types of Pikmin to continue to the Subterranean Complex and Frontier Cavern.