You'll see pictures of the Red Lotus Sea all over Udon as it's touted as one of the province's top attractions, but few Westerners make it there. The trick is in the timing. The sea of lotuses is a spectacular sight, but if you go when they're closed up, you'll probably be disappointed. December to February is best, and in the morning (before 11am), but even outside of those months you might see them if you go in the morning.
You need to hire a boat (400B) to go out into the middle of the lake for the best views. The tourist office can advise on the best times.
The Red Lotus Sea is not serviced directly by public transport. It's in Kumphawapi District. To get there, go along Hwy 22 to Ban Na Di. You can get a tuk-tuk from Na Di to the Red Lotus Sea for 300B return, including a wait.
