Langton Matravers is about 2km north of the coast. The 3 norths will have met land at a place called Dancing Ledge, at about SZ 00000 76833 (50.59121, -2.00000).

https://en.wikipedia.org/wiki/Dancing_Ledge

The quarry caves at Winspit are worth an explore if you're in the area - they've been used in the set for Dr Who, Blake's 7 and Andor.

https://en.wikipedia.org/wiki/Winspit