What does the gym rainforest mean?

Gym rainforest is actually an adjective. People who work out in the gym are constantly exercising and sweating, which is a bit like being in the tropics. Rainforest is an adjective, which means tropical rainforest. Rain itself is water, and sweat is water, which is the same. Forests mean more, and rainforests mean more sweat. Then the tropical rain forest is very hot and sweaty.