You'll see pictures of the Red Lotus Sea (really, it's a pink water-lily lake) all over Udon as it's now one of Isan's top attractions, but few Westerners make it here. You need to hire a boat (300B to 500B for up to 10 people) to go out into the middle of the lake to see the bloom, and the earlier the better as the flowers start to close up around 10.30am and are completely shut by noon.
The season depends on Mother Nature, but it generally starts in late October and lasts to the end of February; January is often, but not always, the peak time.
The main access point to Nong Han, the lake's actual name, is 40km southeast of Udon city in Ban Dieam; there are so many road signs for it that it's impossible for drivers not to find it. There's no public transport, but half-day trips (499B per person) depart from McDonald's at UD Town at 6.30am. Confirm details at your hotel or call the local TAT office for information as details change year to year.