Udham Singh Nagar is the Terai, the flat, canal-fed strip at the foot of the Kumaon hills that most travellers cross on the way up. Its own interest is quieter and mostly spiritual and industrial: Sikh pilgrimage on one side, the state's manufacturing belt on the other.
Nanakmatta is the reason to stop. Gurudwara Nanakmatta Sahib, tied to Guru Nanak's travels, stands beside the broad Nanak Sagar reservoir, a place of langar, evening kirtan and boating banks that draws pilgrims from across north India. Smaller stops fill out the district: the Atariya temple near Khatima, the Baur and Haripura reservoirs where winter waterfowl gather, and Drona Sagar's mythological tank at Kashipur.
Rudrapur, the headquarters, is the practical hub rather than a sight. Its arc runs from a 1960s refugee settlement to the SIDCUL industrial estate it is today, useful to travellers mainly for its hotels, Pantnagar airport 16 km away, and the rail junctions that feed Nainital and the hills.
October to March is the season, when the Terai is cool and the reservoirs are full of birds, while summer is hot and best spent climbing out of the plains. Think of the district as Kumaon's front porch, worth a half-day at Nanakmatta and a birding morning before the road tilts upward at Kathgodam or Tanakpur.