Saga Farmann

A replica of a Viking vessel, the Saga Farmann, is visiting London for a few days. 
It passed upriver through Tower Bridge at 10pm  and was actually quite difficult to see, being a dark boat on a dark river with just a few running lights. 
It's going back downriver on Wednesday 27th at 4pm, so I might have better luck then. It will be visiting St Katharine Docks until 7th September and will be open to the public. 
IanVisits article about it here.