Spending a night (or more) in a real medieval period castle can be the closest thing you get to experiencing what life was like many hundreds of years ago.
It’s actually not as uncommon as you’d think to find authentic castles that have been converted into hotels or other accommodations. They aren’t always cheap but it can be a real opportunity for something unique. There are way too many to list individually, but these various directories should give more than enough options.
Europe
Historic UK
This index has a whole range of castle hotels through Britain, Scotland and Wales.
Celtic Castles
Accommodations fit for a king, or at least a duke. These authentic castles in Scotland and Britain offer a unique hotel stay.
Castles and Palaces
This site has a huge collection of potential castle hotels, as well as other mansions and palaces that can be rented. Not just the UK either, but she has locations all through Europe. Find castles in Spain, Germany, Italy or elsewhere!
Castle Hotels Ireland
Looking specifically to stay in Ireland, then this is the directory you need to check out. Several locations listed and they are all gorgeous.
Spanish Paradors
Look outside of the UK, and find some very unique accommodations in Spain instead.