Door

Anyone else read Niel Gayman's Neverwhere? thats what this reminds me of.

I was at a military park for the civil war, and there was this domed monument (well there were a lot of monuments but I'm posting this one) with a hole on top. The sun shone through the hole onto the wall, which i thought looked much like a door. It also echoed a lot.

minor editing done, it really looked like this.

Hmm, I should have tried to walk through it (maybe I'd get back to Hogwarts).