The Grayling flies from late June to early September; they are especially present in August.
It is a large butterfly that likes to sit on the ground.
The Grayling always has its wings closed.

When they land Graylings snap their wings shut, but raise the forewings so that the eyespot near the apex is visible.
This way, any bird which attacks the butterfly, is likely to aim at the eyespot rather than at the body.
Once the Grayling feels safe, it lowers the forewing to hide the eyespot behind the hindwing.

1st photo: In my yard, Hilversum, The Netherlands, 28 August 2022
2nd & 3rd photo: Laarder Wasmeer, Hilversum, The Netherlands, 9 August 2014
4th & 5th photo: Air Force Base, Soesterberg, The Netherlands, 26 July 2021