If you like wolves or even just like animals, Wolf Haven in Tenino. Oh, and they have a couple of Mima Mounds there, but there is a larger Mima Mounds Natural Area Preserve a little ways west where you can see more of those humpy little geologic wonders, and it's a nice stroll around.
If you like birds, Nisqually Wildlife Refuge. It's an easy and pleasant place to walk. That is kind of on the way home, so maybe a good last stop.

There are lots of nice restaurants and coffee places in downtown Olympia. You could go find San Francisco Street Bakery or the new Left Bank Bakery for goodies to bring back to your cabin.

Downtown Oly has an artesian well in a parking lot by Jefferson and 5th, although sometimes there are odd people hanging around. Worth a quick drive-by or stop, just for the Oly-ness of it all. It's a constantly running tap, so you can fill up your water bottles (at your own risk, as it's not city water, it's straight from the ground).

What else? Lattin's Cider Mill maybe? That'll take a little drive through the hinterlands of Thurston County. Although you can find the cider in the stores around there, like Bayview Thriftway.