Wat Ban Na Kha is in my opinion one of the best temples in Udon Thani to visit. The temple is next to Ban Na Kha Silk Market which makes for a two-for-one sightseeing trip and the short journey there even more worthwhile. The main feature and eye-focus is the Golden Buddha sat atop the Wat but there are some other interesting things to view in the temple compound and inside Wat Ban Na Kha itself. About 15 min And then continue to travel to Nongkhai.
You can also visit the Silk factory show at the same time