Any visitor to Portsmouth could be forgiven for not realising that they were on an island.
The island in question is Portsea Island; according to Wikipedia, "Portsmouth is situated primarily on Portsea Island and is the United Kingdom's only island city, although parts of it have expanded onto the mainland in recent years ... The island is separated from the mainland by Portsbridge Creek which is crossed by three road bridges ([including] the M275 motorway ... ), a railway bridge, and two footbridges".
Portsbridge Creek is less than 100 yards wide, and significantly narrower in some places (e.g. where Portsbridge Roundabout connects the A3, A27 and A397 roads). Portsea Island separates Portsmouth Harbour (to the west) and Langstone Harbour (to the east). Beyond Langstone Harbour is Hayling Island, with Chichester Harbour east of that.
© Haydn Thompson 2017