Four Crosses is a portal dolmen, with three uprights supporting its capstone. It was restored by the landowner in the 1930s, who seems to have accidentally restored one of the uprights as the capstone.
Don’t try to find the footpath marked on the OS map, as it is no longer there (it’s now under a nursery). Instead, park in the layby opposite the nursery, and walk down to the farm turning (named Cromlech, handily). Down the lane, and turn right through the gate opposite the farm buildings.