what about a day trip to akyaka ,thats not that far away and is a very pretty turkish resort, lovely beach, nice riverside surrounded by mountains, its 20 miles from marmaris but nearer to dalyan

http://www.akyaka.org/index_eng.htm

http://akyaka.com/index.php

The famous mud baths are right outside Dalyan as are Kaunos ruins. You can also get a jeep safari or go on a 12 island boat trip. Most trips along the coastline served by Dalaman are available whichever resort you are in.

I think a must if you haven't been before is saklikent gorge.

Then there is white water rafting up the Dalaman river and I'm seriously thinking of quad biking this year ....

Thx folks: Keep 'em coming!
Is Akyaka dolmus-able?
How far is the gorge from Dalyan?

Not sure about the more physical activities you've mentioned as we're not spring chickens anymore , but will certainly be looking into those other suggestions.
Thanks again

im not sure , theres certainly dolmuses to mugla and marmaris to and from akyaka, they might do an organised day trip there, i know its not that far

saklikent gorge is about 2 1/2 hours away i think but ellie meg maybe able to give a more true time scale