Re:what to do with the loops
if not a tunnel
how about some sort of stone cut and planting-ie a stone 'gorge', retaining wall , or the like, if you will for one third of the end (plenty of overhang clearance)-tie it in with your existing back wall-perhaps a pedestrian overpass, or path with fencing, or some sort of flume or pipe just for interest -the stones could explain why the change in curve
and a nice shrib arrangement-thats a smallish shrub
i think it would add a lot of interest without being trite or having some centered item as the 'hub'-even a small pasture, field, garden, very small hut etc