The old town of Mandi is walkable end to end in twenty minutes. From the Indira Market at the centre, almost every temple worth visiting is within ten minutes' walk, including Bhootnath, Trilokinath, Panchvaktra and the Victoria Bridge. Tarna Devi adds a short uphill climb to the same circuit.
For Rewalsar Lake, Prashar Lake or Janjehli, hire a taxi from the bus stand or the Victoria Bridge end of the bazaar. The shared jeep system also runs to all three, slower and cheaper. For Rewalsar specifically, HRTC buses leave hourly from the central bus stand and take an hour each way.
The roads are narrow and the local drivers cheerfully push past oncoming traffic on blind hairpins. If you are uncomfortable with mountain roads, sit on the inside (left) side of the bus and look at the cliff face rather than the drop.