Entrances to the college are marked in red and the flashing yellow square is the sports hall / swimming pool and gym block.
The entrance to this block is towards the back of the college (the Camden Row end), underneath the redbrick arch/tunnel.
That will make perfect sense when you see it.
The Male changing room is on the ground floor and the Female changing room is on the first floor, beside the hall.
The stair leading up to the hall is near the pool and is covered in metal diamond plate, the other stair near the entrance leads to the main college classrooms and is obviously there just to confuse people.
