This happened a couple of weeks ago June 12 2019 at 3:30 pm central standard time. My daughter, (15yrs old), myself and a friend of mine were travelling across the Memorial Bridge on our way to Mandan ND. As wee reached the center of the bridge my friend and my daughter were looking our over the bridge (looking north) and suddenly told me to “look at that!” There was a bright white light hovering midair pretty much lined up with the bridge about half a city block out from the bridge itself. This light was roughly 5 feet in circumference and as our attention was directed at it, it started opening up in the center. my first thought was “omg that’s a wormhole! a dimensional portal!” It kept spinning and expanding til it opened up roughly 4 times its size, the center was a cloudy spiral looking thing that had squiggly lines that extended from the center to the edge of it they started out kinda lightening like looking and straightened out til they resembled bicycle spokes. It held this shape for roughly 5 seconds til it started closing back in on itself til it was the same size that it had been when we noticed it. it then held that size for a second then blinked out on itself. I quickly looked around for other cars on the bridge and was shocked to see we were the only ones who had slowed down enough (that I’m aware of)and were watching this thing. we pulled off the bridge and parked underneath it and waited for like a half hour scanning the area hoping we would see it again. when we got under the bridge we noticed no boats on the river, no body flying kites, fishing off the banks of the river– nobody that we saw who could have witnessed this strange thing. But we all did draw and document what we saw. Not comparing notes til after each of us were done as to not influence the other persons writing. And everyone’s drawing, and description was the exact same minus my daughters depiction which had an odd additional feature…she claims she saw Roman numeral type lettering on the outer edge of the object. (she drew this in her depiction) neither my friend (Bri) or myself saw this. I included all of our drawings and what not that we did as we sat under the bridge immediately after this encounter. all of our car windows were down when this occurred and nobody heard any noise associated with it or smell etc.