Derby Castle Terminus is the southern terminus of the Manx Electric Railway. It is located on the north side of Douglas, Isle of Man; Douglas Station on the Isle of Man Railway is located on the south side of town, with the MER station being termed "Derby Castle" to differentiate between the two.

The Manx Electric Railway is an electric interurban tramway connecting Douglas, Laxey and Ramsey in the Isle of Man. It connects with the Douglas Bay Horse Tramway at its southern terminus at Derby Castle at the northern end of the promenade in Douglas, and with the Snaefell Mountain Railway at Laxey. Many visitors take an excursion on the trams. It is the oldest electric tram line in the world whose original rolling stock is still in service.