You move out of the underbrush and onto the road. To the right, you can see the road follow the curve and flow of the river till it turns out of your sight. The archway is an imposing edifice. The natural rock arch has been cut in such a way that it appears to have been built of large blocks of stone.
The 'keystone' has what appears to be an unfamiliar heraldic crest, a circle in the center bearing a symbol inside of it, backed by a boar's head facing left and a bull's head facing right, which is surrounded by an odd six-pointed shape with graceful curves joining point to point. At the base of each leg of the arch sits a statue, to the left a bull, and to the right a boar. They are facing each other.
The arch itself is quite deep, beyond which you can see that there actually is a gate, currently open such that the doors are flush embedded into the walls on either side. As you step forward, there is a sudden deep tolling sound. As the echos die, you hear some metal-against-stone sounds, and then a voice booms out, "Who goes there?"