About 20mm across.
No interactions present.
Lat/Lng: 51.728091430149, 0.56317806243896
OS grid ref: TL771063
Take The Ridge north away from the 414 towards Little Baddow for approx one mile until you begin to round a tightish left-hand bend. Turn left down the very narrow lane for half a mile and the entrance is on your right. Enjoy.