I don't think horses because in the UK, the tracks tend to be quite large, including the buildings (which are taller to allow for views), even in the most rural venues. For example, this is the small racecourse in my home town (Salisbury):https://www.salisburyracecourse.co.uk/wp-content/uploads/2019/12/Meeting-8-1024x683.jpg
and Lingfield Park is huge by comparison. Plus (I should have been a detective!) the rails at racetracks are white, so the horses can see them.
I think it's a 'people venue'. Maybe a local cricket pitch in winter? The buildings look like changing rooms.
Maybe we should have a thread for "mystery of the day"!