Please Note: The description provided here requires a two-vehicle shuttle. You will begin at the Chapin Creek Trailhead and come out at the Lawn lake TH. The Old Fall River road, is a graded dirt road. Though many if not most passenger cars can negotiate this road successfully, you'll be more comfortable in a higher clearance vehicle.
The Chapin Creek TH is located on the "Old Fall River Road" in Rocky Mountain National Park. This road is One Way, uphill from the access point. From Estes Park, follow HWY 34 or the bypass west to the Fall River Visitor Center and entrance station. Continue west on HWY34 about 2 miles to an intersection just past Sheep Lakes. Turn right onto the Fall River Road and almost immediately right again into the Lawn Lake Trailhead parking area. Leave one vehicle here.( If coming from Grand Lake across Trail Ridge Road, at Deer Ridge Junction, turn left onto HWY34 and drive under two miles to the intersection with the Fall River Road where you will turn left, then right into the parking for the Lawn Lake Trail.) From the Lawn Lake TH, continue driving west to the end of the pavement at the Endovalley picnic area, another 2 miles. Continue almost another 8 miles on the graded, single lane dirt road to the Chapin Creek trailhead. This is where your very long hike will begin. When you eventually return to your vehicle, you will have to continue driving west to the Trail Ridge Road Visitor Center and then drive back down to Estes Park on Trail Ridge Road, assuming you came from the Front Range. If coming from the west slope, you can continue west on HWY 34 to Grand Lake and beyond.
There is no "at-large" camping allowed within RMNP, neither can you camp overnight at any of the trailheads. If within park boundaries, you must camp in the designated campgrounds. The nearest park campground is the "Aspenglen." Check the park website for additional information about which campgrounds allow advance reservations and how to obtain those.