OK -- the obvious natural things to see here are what make the region unique. St. Louis is at the confluence of three rivers, one of which is arguably the world's most famous. How about a trip back in time to the land between the rivers? It's a day trip but it's one worth taking over and over.
Look at this map, I modified it for you:
At the bottom you see north St. Louis and St. Charles. You can see the Missouri confluence just below Wood River IL. in the lower right corner. Here's a paradox: St. Louis is an Interstate hub with Interstate highways 55, 44, 64 and 70 all going right through the city. You'd think you could get around except for rush hour. Now look at the area I shaded green. Notice there's a bridge across the Mississippi at Alton IL. (The Clark bridge -- it's magnificent). The next bridge across the Mississippi is at Louisiana MO. That's over 80 miles with no bridge across the Mississippi. Now look at the Illinois River. There's a bridge at Hardin. Further up where you see Boyle, there's no bridge. The Kampsville Ferry will take your car across the river there.
So think now -- how do you get to that green shaded area? Notice there's not much in there. So, right there on the edge on a metro region of 3 million people Is this chunk of land about 70 miles long and from 5 to 15 miles wide that is nearly empty! It's inaccessible. There's the little town of Brussels near the river confluence. Visiting Brussels is a trip back in time. Plan to be in Brussels in time for dinner at the Wittmond Hotel:
Welcome to the Wittmond Hotel. Notice Swan lake -- you want to photograph waterfowl? That's the place. The region is hilly and driving can be adventurous at times to go between the rivers. The region is stunningly beautiful and of course very rural. There are more nature reserves along the two rivers than you can count. If you want to get out and walk in nature you'll have ample opportunity.
Take the Alton bridge across the Mississippi and head north up highway 100 to Grafton. I marked Grafton on the map. The state maintains a car ferry just north of town which will take you across the Illinois river; it's free and runs pretty regularly. Now the only way out is the bridge at Hardin 22 miles north, back across on the ferry, the bridge all the way up at Louisiana, or, if it's running, the Golden Eagle ferry across the Mississippi. The Golden Eagle is private and will cost you about $10.00 and it's not too reliable.
Take Care,
Joe