This gorgeous place is more like a scattering of villas than a hotel and is perfect if you want nothing more than to chill in the sun by the pool, with an amazing view and surrounded by the sound of cicadas. I did, so it was perfect! Definitely try to get a suite with a sea view. There are two pools, one of which is an infinity pool overlooking spectacular rolling hills and the sea.
Beds are really comfortable - memory foam pillows! - and rooms cleaned/fresh towels etc daily. The honesty bars are well stocked but it's cheaper to put your own booze in the fridge there or in your room.
Real mix of people: couples, families, friends. Definitely no groups of party people! You'll need to hire a car the whole time you're here: if you're not having the (quite expensive) breakfast then the port is a 2 min drive away where there are several breakfast type places. In the port there is a restaurant with a sandy floor on the right by the sea which does amazing, and cheap, salads and pasta. Do NOT go to the fish restaurant: overpriced, mediocre food and poor service.
Cas Pla is about a 10 min drive from wonderful Benirras bay - amazing sunsets, drummers, dancers, and a lovely cool restaurant called Elements: seriously delicious food and not as expensive as you might think. The north of the island has such a peaceful, chilled out vibe, which Cas Pla massively contributes to. San An and Ibiza Town are only a 20/25 min drive away but if you want rustic luxury, a pool to yourself even in high season, windchimes and to feel as though you're guests in someone's enormous home rather than in a hotel, this is for you. Absolutely loved it.