I read up on chestnuts and made sure I picked the edible ones! These are the sweet ones which are encased in a prickly green covering. Stand on the prickly ball which is somewhere between a golf ball and tennis ball size - this sort of splits at a seam and lets you dig out the chestnuts. When split open you get up to three chestnuts but mostly two decent sized ones and a 'sliver' of a third which you probably will discard.
If you forage your chestnuts, make sure you use the correct sweet chestnuts, NOT horse chestnuts.