The tunnel is an old symbol for a passage. On photographs they also make good models: Symmetry, interesting shape, often intriguing details.
I love this one in particular. It always reminds me of the fact that even if you do not see the exit and it looks like a dead end, there are plenty of exits to this tunnel – always. Why would there be a tunnel?
Feel free to use this picture in your presentations or any other work which is not for sale.