Any collection of sycamores probably has this someplace, sometimes on the ground and sometimes on dead branches as this piece was. Even when it's above head height it will invariably have the tooth marks of mice as they apparently find enough nutrition in it to make it worth gnawing.
All that's visible on the surface is the stroma (the dark patch) and the ostioles - the little tubes through which spores escape. Cut the surface and you can see the little spheres where all those spores are developing.
Down inside the engine room, where the spores are being developed ...
This lifestyle's a remarkably successful one. There are enough species of fungi like this to put them up alongside the birds and the fish.