My friend's family has been going to Acadia every summer for probably 15 years, and myself and other friends would tag along and have a big ol' fun time. And every single year, we stay at the Blackwoods campground. You would think I'd have more pictures, but there's so much to do around the site that you forget to document!
The campsites themselves are usually completely booked throughout the season, so make sure you plan and book in advance. However, never have I once got the feeling of things being really busy of overrun with people. The sites are decently sized and well taken care of. Even though there are a ton of individual sites, you really feel like you're in the forest and each site is separated by dense trees, giving you the feeling of peaceful solitude. The campsites themselves are pretty standard; fire rings, picnic table, flat ground for tents. Bathhouses are always in walking range. I think quarter showers are in select ones (though you don't need it--splash around ion Hunters Brook where is crosses route 3. You can even jump from the road when it's deep enough!). What I really like about these sights are the intermingling of trees, making good bases for hammocks, slacklines, and whatever things you need to hang between trees.
One of the best parts of staying in the Blackwoods campground is the proximity to the cliffs over the ocean. From Loop A, there is a little trail that takes you to to Park Loop road. Cross it, and you're on some rocky cliffs over the ocean. Amazing views. Awesome for bouldering too, if you're into climbing. And one night every trip, my friends and I bring our sleeping bags and sleep on the rocks over the ocean. 10/10 would recommend. Just make sure you're above the high tide line! The stars are unbeatable, as well as the sunrise. We really stay at Blackwoods campground just for this being close by.
The Camp Penacook Shelter is a nice stopping point on a moderately difficult hike up to the peak of Mt. Chocorua. As you head up the Piper Trail, as you're nearing the 3 mile mark, it starts to get steep and mostly stone steps. Luckily, right as you begin to tire, the branch for the Spur Trail appears! A little bit down this trail, and boom, you can see the Camp Penacook shelter tucked away in a little clearing with a vista.
This is a 3-sided shelter with a fairly low roof. You could fit one larger tent or two smaller tents, but I highly suggest sleeping in the open air! When I stayed here, there were 7 of us, and we comfortably laid side by side with our packs tucked against the back wall. The roof peaks in the middle, and it was nice to have the extra space in front of the shelter that is still covered by the roof (it was a little drizzly the morning we left). There is a fire pit with a grill rack, but I highly recommend a personal camp stove for reliability.
Back towards the main piper trail is a brook where you can pump water if you have a filter. It can be hard to determine where the bank is if there's still snow on the ground, so be careful! But the proximity of the stream was very convenient. Also nearby the shelter is a pit toilet. There's a social trail down to the toilet which is kind of tough to spot, so make sure you find it in the daylight! And bring your own TP.
The Camp Penacook Shelter is a first-come, first-serve deal, so get there first! It's not really out of the way, so drop your big packs off in the shelter to mark your spot, and then finish the hike to the top with just your water bottle (and camera!). The mile and a half to the summit is scrambles up some slick rock, which can still be icy in spots in the spring. It was very helpful that I removed my pack to do this! The views from the summit are breathtaking, and with a place to sleep not far below, you can stay at the summit as long as you want. This shelter has many amenities for being stuck on the side of a mountain, and I highly recommend making the trip with some friends.