Botolph's Priory in Colchester, is a fairly in tact ruin from 1100 which you can visit for free!
The structure is seriously impressive, given how old it is. It's an example of early Norman architecture. It was built in flint and reused Roman brick.
You can access this sight through Priory Street, and the nearest car park is Britannia Car Park, off St Botolph's Circus. Please be aware before visiting that there are no facilities on-site.
Colchester is home to a variety of historical sites, so if you enjoy exploring British history then it's the perfect place to visit!
Concessions: Free entry