Roos Hall

You're looking at what remains of a proper medieval stronghold, though calling Roos Hall a castle these days feels generous. The ruins sit just outside Boston and what you get is a chunky gatehouse from the 14th century - brick built, stern-looking, the sort of structure that meant business when it went up. It's not the romantic turret affair you might imagine; this is functional fortress architecture, deliberately made to intimidate.

Walking around the site gives you a real sense of how castle architecture evolved. The thick walls, the narrow windows, the way the structure is built to withstand serious medieval siege attempts - it all becomes obvious when you're stood next to the actual stone. There's not much to do here in terms of tourist facilities; you're looking at maybe 20 minutes, tops, unless you're really into military history. No cafe, no visitor centre, just the gatehouse and whatever ground level access you can manage.

Historians will find it worthwhile. Families with young kids might struggle unless they're genuinely keen on castles - there's not the interactive element you'd get at something like Lincoln Castle. Solo walkers heading through the area, though, should absolutely factor in the short detour.

If you're based at Long Acres Touring Park five miles away, this makes an easy morning excursion. Boston itself offers more substantial attractions, but Roos Hall scratches that medieval itch without eating into your day.