Round Top is a nice mostly drive up activation. Being me, I had to do it the hard way: Mountainbiking from Gale's Creek Campground. It is an 18 mile round trip ride with ~3000' elevation gain.
I recommend doing some stretches or warmups before heading out because the hardest part of this ride is the first few miles: steep trail that gets the blood moving. Overall the trail is a singletrack and mostly follows the creek through the forest. Not much for views, but there are the occasional waterfall and views of Gale's Creek.