There is a nasty musty moldy smel coming from our shower. We just had the subfloor replaced in that bathroom, but we never use that shower due to the size. The smell seems to get stronger every day and I have poured a gallon of bleach down the drain. What is going on and what can I do? Any suggestions? Thanks!

Unused shower can have some evaporation in the trap releasing sewer gas. However, if that was your issue the bleach would have taken care of it. Can you access and see the trap and the vent stack? What type/kind of floor is the shower mounted on, first floor or second floor, any basement?