Zundbridge

About 10 miles southeast from waterdeep, where the Trade Way crosses the Dessarin.

there is a Waterdeep guard post, a campground, and a water pump. Don't magically mess with the bridge, it's rumored to be a stone golem of some sort.

As for it's size, it only says that it is squat and massive. From the picture in the Volos' Guide it looks about 15 to 25 feet wide feet wide.

Volos' Guide guide to waterdeep