Appleby Castle is in the town of Appleby-in-Westmorland overlooking the River Eden. It consists of a 12th-century castle keep which is known as Caesar's Tower, and a mansion house. These, together with their associated buildings, are set in a courtyard surrounded by curtain walls. Caesar's Tower and the mansion house are each recorded in the National Heritage List for England as a designated Grade I listed building. The uninhabited parts of the castle are a scheduled ancient monument.

Appleby-in-Westmorland is a market town and civil parish in Westmorland and Furness, Cumbria, England, with a population of 3,048 at the 2011 Census. Crossed by the River Eden, Appleby is the county town of the historic county of Westmorland. It was known just as Appleby until 1974–1976, when the council of the successor parish to the borough changed it to retain the name Westmorland, which was abolished as an administrative area under the Local Government Act 1972, before being revived as Westmorland and Furness in 2023. It lies 14 miles (23 km) south-east of Penrith, 32 miles (51 km) south-east of Carlisle, 27 miles (43 km) north-east of Kendal and 45 miles (72 km) west of Darlington.