Technically, tortoises can be found in pretty much any space where there are cattle, because they love pastureland, but these of course are not open to visitors. In terms of formal places to see a tortoise in the wild, Santa Cruz has El Chato Reserve as well as the Giant Tortoise Reserve - aka Rancho Primicias. Rancho Primicias is essentially right beside El Chato and similarly has lava tunnels, wild tortoises, coffee, birds to observe, walking trails, and a restaurant. They both come well-recommended, so you will have to simply decide which one seems better to you. If you have lots of time, you could also go to both El Chato and The Giant Tortoise Reserve!
In my case, on both my visits to Santa Cruz I have only ever visited El Chato Ranch, and I have loved it both times, so I can personally recommend it as a great option to see a wild tortoise!