Where is Doi Suthep? What is the best way to travel to it?

Wat Phradhatu Doi Suthep is located above Chiang Mai, East of the Chiang Mai Zoo.

The easiest way to arrive is to rent a red truck for 200-300 Baht from anywhere in Chiang Mai City to take you all the way up the mountain by yourself. Just tell the driver "Doi Suthep". From the airport you can take a taxi for 360 Baht.
The more affordable way is to take a red-truck to the Chiang Mai Zoo for 15-20 Baht, then wait for the red trucks there to go up the mountain with other passengers for 40 Baht each. This is only possible during the day until 4 pm.
Once you have arrived at Wat Doi Suthep, you can climb up the 306 stairs from the road or take the elevator.