Callendar House is a large French Renaissance-style mansion at the edge of a country park east of Falkirk town centre. The original fortified house dates from the 14th century, though what you see today is largely a mid-19th century remodelling. The interior houses the local history museum for Falkirk, but done properly — rooms are furnished in period style from different eras of the house's history, so you walk from a Georgian kitchen to a Victorian parlour to a room exploring the area's industrial heritage.
The park around the house is free to enter and pleasant for a walk, with a loch, formal gardens, and paths leading into the Callendar Woods. The woods contain the Antonine Wall, Rome's second frontier in Britain, which you can walk along here. The Forbes Mausoleum — an early 19th century structure now locked and atmospheric — is in the woods too, and worth finding if you enjoy a little carefully managed decay.