Two lighthouses mark the outer harbour of Castletown. One is at the end of Irish Quay and the other on the New Pier.
A red buoy marks the Lheeah Rio Rocks on approaching the harbour. The breakwater lighthouse forms a transit with the Irish Quay Lighthouse to guide vessels into the inner harbour. A green metal column marks the north side of the harbour. The inner harbour dries and has is a swing bridge.
In 1765 a lighthouse was built at Castletown harbour entrance. Whenever a ship entered the harbour, a light was shown. A light was also exhibited throughout the herring fishing season.
The current lighthouse on the end of Irish Quay was built in 1944.
In 1845 a new pier was built from the west side of Irish Quay forming a new Outer Harbour. The New Pier was extended in 1849 and a wooden lighthouse was erected at the end. A 30ft high tower later replaced this one.
Castletown was the capital of the isle of Man until 1869. It is dominated by the medieval Castle Rushen.
The Manx Nautical Museum is located alongside the harbour wall. It was built by George Quayle and has secret passages and doorways. A secret passage can be seen across the water from the harbour and was used for smuggling goods.