The historic fort is part of a navy-run resort. There's a restaurant right on the waterfront with great views of the fort. It's a big place with a big menu and is a good stop for lunch. It's open to the public and is 1km west of the Kayts ferry jetty.
Because it's inside the naval base you need to present a copy of your passport for access. There are hotel rooms out on the fort, but they are restricted to people who have made reservations 'through an admiral', as the management explained.