So I was looking at my friend's base and he was raided I noticed a weird grid under his Destroyed Town Hall. It's a square grid that starts from the outside with the color Yellow and gradients it's way to the inside to red squares. Any ideas what this is?
When a level 10 Town Hall is destroyed, the ruins are lying on a grate on top of lava.
Also, it is stated that
The lava in the level 10 Town Hall may be a reference to the fact that the Inferno Towers are unlocked at this level.
So, basically it is a metal grate (probably on which the town hall is placed) and below it there is lava.