This lake near Luodong isn't very big, but it's worth a visit if you're in the area. The lake is extremely popular on weekends, so it's not the place to get away from it all and commune with nature. But on weekdays it's usually fairly quiet.
There's really nothing in particular to do here - it's just a pretty place. Most people just stroll around the lake and enjoy the scenery. You can also ride a bike around the lake. But it's so small that you can zip around the lake really fast. If this is your main destination, it's probably better to walk and stop several times at the lakeside pavillions to take in the scenery and relax.
The lake isn't far from the Lanyang River Bike Path (see my post). You can rent bikes from shops on the road in front of the lake. To get to the riverside bike path, you ride down the access road to the lake and turn left at the corner. Ride uphill and cross the traffic roundabout. The bike path runs along the levee on the south bank of the river. This bike path connects with several other bike paths, so you can ride quite far in several directions from here.
There are some shops lining the road leading to the lake which sell snacks and drinks. The specialty seems to be a special Taiwanese sweet which consists of ice cream and shaved peanut brittle wrapped inside a pancake. If you've never had one, it's definitely worth trying.
The lake is in Dongshan township, next to the foothills southwest of Luodong. To get there from Luodong, just take a road in the general direction and follow the brown signs to the lake. Road signs aren't Yilan's strongpoint, so I'm afraid it's not possible to give better directions than this. If you're afraid of getting lost, you can just follow the road next to the Lanyang River upstream. Turn left at the roundabout and go downhill to the lake. There is a huge temple on a mountain above the lake. The temple is easily visible from a long distance, so driving toward the big temple might help you get there.