Entrance to Western Heights hilltop fortifications

Nice old fort. The passage quite low, but great view

Drop Redoubt fort is linked to the citadel via dry moats. You can look round the exterior of the fort for free at any time during daylight. The fort is located on a cliff with a steep drop into the sea but was actually built to defend attackers from inland who had invaded from the other side of Dover.
Drop Redoubt is in the care of English Heritage with occasional guided tours available. See their website for more details english-heritage.org.uk/visit/places/western-heights-dover

One of the most important and impressive fortifications in Britain, the Western Heights are a series of strong points linked by miles of ditches