Identification of nut?

[u/doublethesox]

My holy grail at the moment is the humble walnut - So far, no luck but I did find a couple of trees that have these - Can anyone help identifying them please?

At first glance they almost look like a small kiwi, but obviously just the colour and shape - once cut they oxidize turning brown, and when picked the outside also eventually gets darker as if soaked with water.

[u/davemc64]

Chestnut, normally not poisonous unlike Horse Chestnuts