Sleeping in this apartment (which is absolutely enormous!) felt like a stay in a museum. It's HUGE, and the terrace could easily host 100 people. We did yoga on the roof and enjoyed breakfast on the terrace. We loved the space, the washing machine was helpful, the bathroom was modern and clean. Castellana is a gem of a town, perfect for exploring the nearby towns but without all the tourists. You MUST visit the Osteria del Caroseno for a truly memorable meal, and check out the historic center to see what the valley towns were like before tourism.
Downsides: There is significant street noise that woke us up early each day. Check-in took more than 2 hours and after that long delay, we found out the second bedroom was completely locked up, so we couldn't access it. We waited another hour to have the room opened (cannot imagine why this room isn't always open, when the property is listed as a two bedroom). ALSO: you must take out your own garbage or pay a 10 euro fee. We had to drive the garbage to the "blupoint" (recycling), about 5 minutes away. With these inconveniences, we still loved the space very much, but note it's being run a bit impersonally by a company, rather than an individual.