Casa Zen is a wonderful place to stay! The building is nice and got an asian touch, situated in a small garden. The owner Kelly, is a great person, who really cares for her guests and is always helpful, as is the whole staff at Casa Zen. The rooms are simple, but homey and the beds are comfortable. There are no private bathrooms, but the communal showers and toilets are always spotless and there are a lot of them, so you don't have to wait in line.. ;) Casa Zen is close to the beach (1 minute), but if you want to surf, the better spots are 10-15 minutes walking distance. If you don't feel like surfing, you can just relax in one of the hammocks on the wonderful Yoga-Deck! You can do daily Yoga classes there as well, which are really nice, too!
Though the restaurant of Casa Zen closed recently, you don't have to worry about getting enough to eat. There are a number of great places around ("Casa del Mar" has great barbecue, "Rancho Burger" serves delicious fish and other dishes) and you can use the former restaurant kitchen as a communal kitchen now, so that's really well equipped.
We stayed at Casa Zen for a whole week (extended twice, because it was just so nice!) and would definitely recommend the place to anyone, who looks for a friendly, nice and clean place in Santa Teresa!