I'm not sure about the trolls, but they are in the painting. This mural can be found downtown Hastings. I believe it is on the side of the Scandinavian Marketplace building which can be seen in this photo from an earlier daily photo of mine. The spiral bridge in the mural is actually what the original bridge looked like as you crossed the Mississippi River leaving Hastings.
I've found an archive photo of the original spiral bridge from around 1900. Here is an aerial view of the bridge that shows a lot clearer photo and just where the bridge was located, I'm not sure of the date of this photo. I believe the bridge at the time was for horse and buggy plus people crossing only. I'm not sure when the bridge was torn down for replacement, but I'm sure it couldn't have lasted too long once automobiles started crossing the bridge.
I'm rather curious if anyone knows of any other spiral bridges that are in place or had been in place at one time. I would have to believe this is quite original for it's time. I've never seen another and with today's automobile use, it certainly isn't practical.