This park is conveniently located to several beautiful hiking trails. It is also close to Bellingham, WA. so if you want to go into town for shopping or dining, it is an easy drive.
We hiked up to "Fragrance Lake" which is a small but gorgeous lake (5 miles round-trip; some elevation gain). There is also the Oyster Dome hiking trail nearby (I have not done this one yet).
You can find details on both hikes at the Washington Trail Association website http://www.wta.org/go-hiking/hikes/.
Caveat: There is a train located very close to the campground. The park has done a good job of putting signs up indicating which specific camping sites are next to the railroad. So be aware of this issue when you are booking your campsite.