The iconic trip in Guilin is to take a boat from Guilin to Yangshuo on the Li River. As you might expect, this trip is very touristy and crowded but it does offer great views of the karst landscape that Guilin is famous for. Often the views have other tour boats in the foreground! If you want to avoid the crowds, then you can also hire rafts with a boatman to take you on the Yulong River. The scenery is similar to that on the Li, though not as spectacular I guess.
We decided to spend one night in Guilin so we could take the boat ride down the Li River. However, we made the mistake and got scammed in that our ‘boat ride’ on the Li River was actually a bus ride from Guilin to Yangshuo with two short rides on boats along the way, and a 2 hour stop at a jade store to try to get us to buy jade. So beware of this scam. You can see photos and travelogue, along with info on our mistake here neurotraveler
Have a great trip!