Greg is correct, but there are a couple of other options.
The closest parking to Lumpy Bumpy is that Parking marker just north of LB on the map. This is a small dirt lot (approx 5 cars) off of Cranberry Ledge Road. Take Route 206 and make a left if heading north / right if heading south onto North Shore Road. Approximately 1 mile up, make the first right onto Cranberry Ledge Road. Follow that for several hundred yards and you will come up onto the small dirt lot. It's a quick 10 minute ride to LB.
Personally, I would park at the Parking marker at the northern tip of the lake (this is the Park n Ride). Take the Sussex Branch trail along Route 206 for a hundred yards or so and as you are about to ride up to a house that sits in-between Route 206 & the Sussex Branch, hang a left on to the Green Trail (Wavin' Willy). This is a super cool trail that gets your legs/lungs warmed up for LB.
Just my $0.02
Have fun!!!