A vast subterranean command bunker beneath the Exchange Flags building, from which the Royal Navy directed the Battle of the Atlantic between 1941 and 1945. The Operations Room, with its huge map table, charts and balcony from which the Wrens worked, is preserved more or less as it was when the war ended.
The museum spreads across some 50 rooms — coding rooms, teleprinter rooms, sleeping quarters, the admiral's office — and walking through them is a surprisingly intense experience. Allow two hours; there is a small charge for entry. One of the best-kept secrets in central Liverpool.