Multi-Spa has two locations near the gultch--one in the Radisson and the other on Calle 2 between Av 4 & 6 (near Parque Central and the Park Hotel).
The Radisson location has a pool. The Calle 2 location is easy walking distance from the gultch and has a good selection of equipment (by CR standards).
Don't know what the daily workout rates are but the monthly charge is c11,000. They gave me a complimentary weekly pass when I first moved down here.

The Calle 2 location is also over a tico bar (the 3rd to 6th floor).