The B150 runs to the north of Finsbury Park in north London.
It starts on the A1201 Stroud Green Road and runs along Woodstock Road before zigzagging onto Florence Road, then TOTSOs right onto Upper Tollington Park to go under the old Northern Heights line, now a footpath, then cross the East Coast Main Line and reach Finsbury Park. There's a sharp left-hand bend onto Endymion Road which skirts the northern side of the park to end at traffic lights on the A105 Green Lanes.
Florence Road is now one way northbound so it would make more sense for the B150 to be diverted along the whole of Upper Tollington Park to avoid this. Current maps show this has not happened.