Sizergh Castle sits just outside Kendal, close enough to the Lake District proper that it's easy to combine with a wider day, but far enough from the honeypot lakes that it rarely feels crowded.
The castle is three and a half miles south of Kendal on the A590, roughly twenty minutes' drive from Windermere and about five miles from Oxenholme station — a convenient stop for anyone arriving by train. It's also accessible by local bus from Kendal. The National Trust car park is generous and rarely a problem even on busy days.
Both the castle and the garden are open most days from March to November; check the National Trust's own website for current hours and admission, as these are set independently and can change season to season. There's a shop and café on site for anyone wanting to make a full half-day of the visit.
For guests interested in medieval history specifically, Sizergh sits naturally alongside the Roman fort at Galava in Ambleside and the medieval remains of Kendal Castle above the town — three sites spanning two thousand years of the same landscape, all within a short drive of each other.
Sizergh Castle can be included in a bespoke history and heritage tour.