Casa Zen has been by far the best place for the value we have stayed in here in Costa Rica. Our room was private double room and was clean and simple - just what we were looking for. There are multiple areas to hang out as well as wonderful hammocks to lounge in.
The breakfast was absolutely perfect - fruit, toast with butter and jam and coffee (or tea). The community kitchen was easily the nicest we have ever seen as it used to be the professional kitchen for a restaurant that used to be there. It was also well stocked with cookbooks and a variety of spices.
We didn't take any yoga classes as we were on a budget but heard from other visitors that they were very good.
Casa Zen was so close to the beach - a 3-min barefoot walk away! It was also well placed in between the sprawling, long road of Santa Teresa. The grocery store was directly across the street.
Overall, an excellent option and the best value you'll find in Santa Teresa!