Where the M25, M26 and A21 meet.
This is taken from the Chevening Road bridge.
The road crossing left (northbound) to right (southbound) is the A21.
The 2 left hand lanes are the eastbound M26 and the slip road for the A21 is just out of sight. The middle 2 lanes are the merging lanes from the clockwise M25 whilst the 2 right hand lanes are the end of westbound M26.
Driving along the M25 for 117 miles in either direction will bring you back here...