Wyoming In September

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Guys, need some help/opinions on my next road trip later this year, in September. The plan is that I fly into Denver with my wife from the UK, pick up a rental bike and set out for a couple of weeks, returning to Denver to fly home again. Thinking about a circular route (in a northerly direction) to include Yellowstone, but not sure where else would be good to include in the route, all sugestions welcome please.