The most rewarding day trip from Parkersburg is straight up the Ohio to Marietta, on the Ohio side of the river, the first organised American settlement in the Northwest Territory and a small river town with several good museums of its own. The drive is twenty minutes.
For nature, North Bend State Park, about 45 minutes east of the city, has a long rail-trail (the North Bend Rail Trail) running through railway tunnels and over old trestles to Wheeling, and is popular with cyclists. Mountwood Park, halfway between, has a lake for fishing and swimming and a good network of mountain-bike trails.
For a longer drive, Charleston is 90 minutes south and the state capital is worth a day in its own right.