When we were living in Boulder, Colorado (2007-2009), we ran the Bolder Boulder 10K twice, but (alas!) races of that length are no longer in our repertoire.
However, as temporary residents (part of May and June, 2018) of the same fair city, we were thrilled to discover that the race route was only a few short blocks from our rental home. It turned out to be a good Memorial Day activity for us. According to the official statistics, there were about 50,000 participants and 150,000 observers such as ourselves.
There were thunder clouds the whole day, but the rain never materialized, and the race and holiday celebration in CU’s Folsom Field came off without a hitch.