The hotel is split across 2 buildings. The first (main building) houses the reception, couple of seating areas/ rooms/ bar dining room, indoor swimming pool and some rooms (with lift access). The second houses more rooms, a conservatory and the outdoor swimming pool.
We stayed in the second building which is lovely. The only downside was that we were on the top floor (3 floors) and this meant climbing the stairs, as no lift in this building, so if you have young children or are less mobile make sure you are clear when booking.
The rooms are clean and spacious and some days we were the only people at the outdoor pool.
The village itself is small, but perfectly formed :). With some lovely restaurants, shops, bars and a few beaches (on which you will be charged approx 25 euros for 2 beds for a day).
Our 5 days here were just enough and I would recommend Castglioncello & Hotel Atlantico.
FYI - Castiglioncello is busier on the weekends as this seems to be a resort where the local Italians visit. Also train travel was cheap & easy :)