Longqingxia We took the S2 train (the same one to Badaling Great Wall) bound for YánQìng [ 延庆 ]. You can just use your subway card. It costs just 6 RMB each way. Get off the final stop, which is 1 stop/20 minutes past Badaling. It took an hr and 30 minutes in total from Beijing North Station's [ 北京北站 ] ground floor by Subway Line 2's XīZhíMén [ 西直门 ] Station.

Outside Yanqing station, we took a taxi for anther 20 minutes right to the entrance of Longqingxia ( map )   [ 龙庆峡 ]. The ticket costs 40 RMB. Once you enter, you walk a bit until you reach the dam/dragon escalator, which is quite cool from the outside but just normal escalators inside.
Once you reach the top, you can take a tourist boat (100 RMB return) that leaves every 15 minutes. The boat takes you down the river surrounded by amazing cliffs and drops you off where you can either hike up to Illusion Pavilion to look down the beautiful valley (quite a long steep hike up stone steps) or walk the other way to rent small paddle boats (50 RMB per boat that can carry 3 people with no time limit). The small boat was quite frustrating to paddle but the view was nice. There are also places to do bungee jumping/zip-line over the river. The last tourist boat back is at 5 pm. You can take a luge back down for 20 RMB. It wasn't very fast but it was good fun. There's also a gondola up to another temple but they stop selling tickets more than 30 minutes before 5 pm.
Dragon Valley
There are restaurants near the entrance/exit and places to buy water/drinks inside. The train back to Beijing is at 5:17 pm or 7:18 pm so time it well. It takes roughly 2 hours to get there from Beijing North Station. You can easily spend 3-5+ hours here. It was not crowded at all on a Tuesday afternoon.