Kodaikanal is small enough to walk across in half an hour, but the surrounding sights require transport.
Walking and cycling work well for anything near the lake. Bicycles are available for hire on the lakeside road; prices are negotiable and a few hours is usually enough for a full lake circuit and a couple of nearby viewpoints.
Auto-rickshaws are available in town and will take you to the main viewpoints. Agree the fare before getting in — there are no meters.
Taxis are the best option for the full circuit of Pillar Rocks, Guna Caves, and Dolphin's Nose, which are spread across the hill and awkward to visit independently. A car hired for the day from the taxi stand near the bus stand will cost around ₹1,500-2,000 and will cover all the main sights. The driver will know the route.
The main road between the bus stand and the lake area has tourist-oriented traffic at peak times. Everything else is quiet.