Umananda — "the bliss of Uma" — is a small Shiva temple on Peacock Island in the middle of the Brahmaputra, reached by a short government ferry from Kachari Ghat. The temple was founded by the Ahom king Gadadhar Singha in 1694, rebuilt after the great Assam earthquake of 1897. The setting is more remarkable than the architecture: the island is barely large enough for the temple, a few peepul trees, and a small crowd of pilgrims.
The ferry takes ten minutes each way and costs around ₹20. Boats run from about 7am to 5pm; the last boat back is firm — don't miss it. Shivaratri in February-March is the temple's big festival, when the island is mobbed. Outside of that the visit is quick and pleasant, an hour at most.