Alien attack?

These have to be the largest toadstools I have ever seen, with the largest (the spotted one towards the right of the photo) measuring a good 18" across. The are growing on a fallen tree in Toward Castle grounds, and there is quite a path worn through the long grass by people going to look at them.

This area of the grounds gets hardly any sun, and the weather has been damp and warm - presumably good growing conditions?

Anyway, they reminded me of an episode in the original Star Trek series - I expected one to fly off the trunk and smother me...