Cefnbrith Carriage is in Glanhanog in Mid Wales. It's exactly what it sounds like: an old railway goods carriage that's been done up to stay in. It's got a 5 Star rating, which means everything works well and it's comfortable, but it's still a converted carriage so the space is clever rather than huge. It sleeps two.
The main thing is the view. You get big windows down one whole side, looking out over the valley. It's very green. There's a breakfast bar right in front of them. You will spend time there.
Outside, you've got a private bit of garden with a patio, a fire pit, and an electric hot tub. You can bring a disposable barbecue if you want one.
Inside, it's one open room with a kitchenette and the bed. The bathroom is separate. It's all modern, with underfloor heating. Everything you need is there. The WiFi works.
The village of Carno is a couple of miles away. It has a shop for basics. There's a pub, The Aleppo Merchant Inn, that does food. For a bigger shop, Newtown or Machynlleth are about a 20 minute drive. They have proper supermarkets, cafes, and that sort of thing.
If you like walking, you're right on the edge of forestry. You can step out the door. The Elan Valley reservoirs and Hafren Forest are within half an hour for more serious trails. The coast at Aberdyfi is about 45 minutes by car if you fancy the sea.
It's part of a small site with two other similar cabins. You can book them together if you're in a group. Parking is right there.
Useful links: Visit Wales Mid Wales and National Trust Wales.