Dressage exercises for small area

I only have a small area to ride in, not sure exactly of the measurements, the maximum it would be is around 20x25.
What are some exercises I can do in this small space? I need something to keep the ride interesting.

Well obviously you're going to be going in a 20 meter circle already so the only thing I can think of at the moment is spiraling. Use your outside leg to push your circle inwards ultimately making it smaller and smaller. Stop pushing your horse inwards when you get to the tightest circle you feel comfortable asking of your horse and then do the opposite, using your inside leg to push your horse back out onto the original 20 meter circle. When you spiral the only things you should be using your reins for are to keep a light contact and keep the horse reaching into the bit, and to adjust the horse's bend. NOT for steering. If I find any other exercises that can be done in such a small area ill be sure to post again! :]

You could do lots of transition practice, halt to walk, walk to trot, trot to walk, walk to halt, etc. You can practice turning down the midline (a short one) and practicing your halt. You can practice your free walk, encouraging him to stretch out at the walk by squeezing with the same leg whenever his shoulder comes back.

I'm in a very similar situation and with a 16.3 standardbred still learning the ropes on cantering and bending. I like to warm up just going around, focus on the corners, bring the horse deeeep into the corner to get them really stretching out. Remember the half halts so that the horse bends then goes straight as possible Figure eights are wonderful tools, particularly the switch in bends. Its a wonderful way to work on signal refinement also. If you can do serpentines try that. I have trouble with them and can only do them if my horse is feeling extreeemely warmed up. Transitions are also key. You can work on those no matter what the ring size. If you have access to them, work with ground poles at the trot. I like placing them right after a trun, so I have just enough time to get the horse straight, then over the poles. It keeps good focus.

Don't forget walk to canter and canter to walk. Those are such wonderful exercises when you can achieve them with 0 trot steps. Its incredibly good for rounding the back. It also takes energy so introduce it and work on it slowly. Walk to canter to walk ... let the horse walk out a liittle, then repeat. When at the walk extend it then collect it. Itll help

Thanks for the replys!
I'll be sure to try those, especially the canter to walk, walk to canter thing, and the spiraling!

Shoulders in/ haunches in is also great as they can be done on a circle. Sometimes I find it easier as I already have some bend to begin with!

Everyone gave some great ideas! I agree with working on those corners and getting your horse nice and round. In the winter/spring I only have a small space to work in as well. It can be frustrating sometimes, but it really makes you work your horse neatly. Try to perfect the circle, go across the midline (as suggested), do transitions and whoas. You probably won't have much room to canter, but take it as an oppourtunity to perfect the trot, both sitting and rising.