On the south bank of the Thames are two brick and concrete buildings shaped rather like squat toadstools or UFOs. These were built in the 1960s to help with ventilating the northbound branch of the Blackwall Tunnel.

Originally air went in and out through grilles in the eaves of the drum, between the columns. In 2010 they were updated so smoke could be extracted more quickly. Now the roof has hatches all around which open up like a waterlily unfurling. They can open in just 60 seconds in an emergency.