More than a place to visit, the Khon Kaen's lake is a nice place to walk around by feet or by bicycle. You can laso rent pedal boats. There is a small park with a bicycles renter who also rent tandems and a pedal boats renter (they only speak Thai) and trails aroud the lake.
This is the most picturesque place in Khon Kaen. It is near Wat Nong Wang, the Khon Kaen best known temple but also the more modest but charming Wat That. There is also a TAT office (tourism information office) just next to Wat Klang.
It's probably the most pleasant area in Khon Kaen and the one with the most interesting visits to do.