Kullu's pre-eminent temple enshrines the Kullu Valley's most important idol, a tiny bronze image of Raghunath Ji (Rama) that lords it over the Dussehra celebrations. The 17th-century temple is on the hill above the bus station and near the Raja Rupi, the former Kullu rajas' palace; it's not particularly spectacular, and the main shrine is closed from 11.30am to 5.30pm (12.30pm to 4pm from mid-September to mid-April), but you will probably still be able to peer in through its barred window.
