where would pan wallow on a rainy day?

Question

im workin on a crossword puzzle for language. its greek and roman mythology. it says "Where Pan might wallow on a rainy day" and i know that it starts with Mu. but whats the 3rd letter. its only a 3 letter word. thanks!

Answer 1

Uh, mud?

Answer 2

will mum work ? (mummius)