This is such a funny response to the title provided. Love how hard you've gone on the horse stuff. Agree with commenter below that visual distinction of hidden paths vs non-hidden on the map would be useful. Reading, I was expecting more explicit guidance on how players might be able to infiltrate and/or win the race, but actually I think there's enough flexibility here to expect that players will come up with something more creative and probably weirder than if it were spelled out as a solution.
The title image art is amazing so wish that'd found a corner of the module itself, but you do have a lot to fit in!