One of the iconic steps along any drive to Big Sur is McWay Falls. A short walk from the road is a spectacular view of a small bay, with water from the river falling 80 feet directly onto the beach into the ocean. However, if you're here for more than a few minutes, the Ewoldsen Trail is a great place for a day hike.
There's pretty much everything great about hiking here - old-growth redwoods, canyons, ocean views, and the aforementioned waterfall. For that reason, the trail sees high usage, with a fine layer of dust covering plants near the beginning of the trail and filling the air on a dry day. Once you get further from the parking lot (and the elevation gain takes its toll), it clears up a lot, and becomes a very enjoyable experience.
Parking is free along Highway 1, or you can opt for the $10 paid parking in the lot.