Advice on using an arena with elevation.?

You could make patterns around the lumps, you could walk and trot up and down (I don't know how big the lumpy areas are). But your right to incorporate them in your exercise-depending on how big or little they are and if they are three hills clumped together or spread out over the center of the arena. You could also go half way up and get your horse to back down straight. Just a few ideas.