As someone above said, the beltway on the east side of Denver is a toll road. And some pretty hefty tolls, at that. If you stay on the beltway all the way around you will never see a toll booth, but you WILL get a bill in the mail a few weeks later.
The bill you get will depend on the number of axles and how far around the beltway you are going. We got a bill for $26 for 1/4 of the way around (I-25 southbound to I-70 east-bound) in a pickup with a double-axle trailer. They pick up the license plate on the toad or trailer and send it to the registration name/address.
