How do you get through ice fall cave in pokemon fire red?

In order to pass into the cerulean cave in Pokemon firered/leafgreen you must first be the elite four champion as well as have found and given the ruby and the sapphire to celio on one(1) island. after completing those tasks go to the cave and the guy will be gone. Inside you can catch Pokemon whose level vary from 40-70 and here is where you also catch mewtwo. If you want to find strong Pokemon(65-70) use a max repel and only those strong ones will pop up