Stonecraft London
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I would say it is a great museum, but the word great doesn't sit well with this place. It's a very chilling and frightening place. Especially when you realise how many yang lives were broken here. Intelligent, talented people that had a different political views were brutally murdered here for years and years. Prison cells that are the size of a normal double bedroom would house up to 30-35 people at times.
Visit it, so you know a bit more about our not so distant past.