I have a one mile cardio trail here in my woods that I built. It is not a fast paced trail because it is very very technical - I guess it could be faster as long as you wore some sort of shin protection - but it has major ups and downs, ravine climbs and slides, water crossings, log crossing and ziggy zagging...right now it is a bit grown over but I've got to get the chain saw back there to some of it. The drought here has caused a bunch of the trees to drop their lower limbs, and some paths are impassable. But even on my own two feet, it is a calorie burner!
RIding a one mile trail over and over can be mind-numbing like the hot walker, but the terrain really builds the rear and the weaving in and out helps keep the horse soft with leg-yields and such so it does have benefits. There is one large perimeter trail, and some switch backs inbetween so you can vary it up just a bit so they don't anticipate where they are going all of the time.....but that's about all I've got right now to work with for my conditioning without leaving the property.
Making the loop five times every day gets pretty boring, that's for sure but it has to be better than a hot walker by far! Right now, it is in the triple digits here and just too hot! What are your temps there? Do you have much humidity that you have to deal with? Or is your area pretty dry?