A significant hole

This is the allotment building that houses the shop around the other side and through this door, the kitchen and toilet.

I'm not sure why there are gaps in the brickwork long this side, the the hole just to the left of the door is now being used as access to a nest by a family of tits and the parents are currently popping in and out at high speed.  So fast that I can't tell which type of tit!!