The Spinnaker Tower is a 170-metre (560 ft) landmark observation tower in Portsmouth, England. It is the centrepiece of the redevelopment of Portsmouth Harbour, which was supported by a National Lottery grant. The tower's design was chosen by Portsmouth residents from a selection of three different designs in a 1998 public poll. It has three viewing platforms one on top of the other at heights of 100 m, 105 m and 110 m.

Portsmouth is a port city and unitary authority in Hampshire, England. Most of Portsmouth is located on Portsea Island, off the south coast of England in the Solent. This means Portsmouth is the only English city not located primarily on the mainland. Located 74 miles (119 km) south-west of London, 50 miles (80 km) west of Brighton and Hove, and 22 miles (35 km) south-east of Southampton; Portsmouth is part of the South Hampshire conurbation. It is the most densely populated city in the United Kingdom, with a population last recorded at 208,100.