Nice job, the algorithm is really effective! I tried this in multiple cities where it ended up recommending very similar routes to some of my established running routes, and even some new combinations :)

Love that your algorithm tries to exclude out-and-backs, I think that goes a long way to make the routes feel organic and appeal to runners. This is really polished and I wish you the best!

One feature suggestion: I wonder if you could have a flag to generate routes starting in parking lots/park entrances in a radius around the starting location. This could go a long way to recommend some common long-run routes where you need to travel a brief distance via car or public transportation but then can get 10-20 miles entirely in the woods.