The Castle can be visited
Guildford Castle

In Surrey, England, are the ruins of Guildford Castle. Its history dates back to the Norman Conquest.
History+
The origins of Guildford Castle likely date back to 1066, when a motte with a wooden palisade and ditch was built after the Norman Conquest. In the early 12th century, the site was fortified with a stone wall, and around 1130, a rectangular keep was added, replacing a wooden watchtower. The first floor of the keep initially served as royal accommodation before being converted into the office of the Sheriff of Surrey and Sussex, and thus a prison, in the 12th century. The castle also served as an overnight stop for royal hunting parties. Kings such as John Lackland and Henry III used the complex.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.2343, -0.5725