Doi Inthanon National Park
This is a place well worth a visit when you are in Chiang Mai; it will not be possible to see/do all the sights and attractions in a single day so cherry pick your favourites. The location is saved to the following map 
Formerly known as Doi Angka, the mountain now bears (since 1899) a shortened version of the name of Chiang Mai's last sovereign, King Inthawichayanon. During his reign, he had, with great foresight, expressed his concern for the forests of the northern hill country as the watershed for all of central Thailand. The modern study of rain forest hydrology has borne out his early convictions and given substance to Thai folklore which describes this hill region as the home of the Phiphannam, the 'spirit who shares water'. Before the King died near the turn of this century, he commanded that his remains be placed at the top of this mountain: his ashes at the summit stupa are visited by thousands of people each year.
It is the highest mountain in Thailand,at 2565 metres (8415 feet), just a little higher than Australia's highest (Mt Kosciuszko) which is 7310 feet or 2228 metres,and although it is relatively cold up top, it never snows there.
Flora and fauna
The various sub montane forest formations at higher elevations are a unique asset of the park. They have dominant species belonging to temperate climate families rather than tropical. The summit area supports the only red rhododendron in Thailand (R. delavayi); it blooms from December through February. There are also two white-blossomed species abundant on Doi Inthanon which are restricted to only a few other sites.
Where mists are persistent, the slopes carry a moist hill evergreen or 'cloud forest' with many epiphytes, plants which live on tree trunks and branches but do not receive their moisture and nutrients from the host tree as do true parasitic plants. Instead, they are nurtured by the accumulation of dust particles and humus around their 'root' area and the moisture retained there, augmented by frequent bathing in cloud and mist. Epiphytic orchids are also abundant, along with lichens, lianas and fern.
At mid-elevations, 800 - 1500 meters, two species of pine are present, Pinus merkusii mixed with dipterocarp in the lower range, and P. kesiya with oak and laurel on drier slopes in the upper range. The pines are thought to be a relic from a prehistoric cooler climatic period when flora from the Sino-Himalayan region migrated southward. At the mid-elevations of the park, much of the forest has been removed by the activities of swidden cultivators and the slopes have converted to fire climax grasslands.
Mid-day temperatures hover about 10 to 12 degrees Celsius during the day (there is a thermometer at the top). Keep in mind that in the wet season, there is near-perpetual cloud there, so you can see little.
From Chiang Mai there is one regional bus line departing from Chiang Mai Bus Terminal 1 (Chang Phueak Bus Terminal). It goes to Chom Thong. No air con, but fans are on the top and all windows and doors are open during the ride. 1,5-2h. 36 Baht.
Just round the corner of the Chom Thong bus station there is a yellow Songthew driving through the Doi Inthanon National Park to the villages in the west. You can use it to the first or second toll booth. 40 Baht. Just before the first toll booth there is a yellow Songthew station. Usually there should be enough people to share a Songthew towards the mountain top. (In Feb 2020 during the Corona virus outbreak the demand was too low)
Note that a lot of other yellow Songthews going up the mountain are from booked tourist groups and cannot be joined with a hand signal.
Hitchhiking worked good when telling the exact destination in the National Park.
The road behind the second toll booth in the direction to the mountain is closed every day from 18 o'clock.
When doing a day trip from Chiang Mai better ask at the bus station of Chiang Mai when the last bus of the day goes back from Chom Thong.
For farangs (Westerners) admission is 300 baht, for Thais 50 baht, and for the car 30 baht.
To get there, you can either drive yourself, hire a car through your hotel or a travel agent, join an organised minibus tour, or be a little adventurous and hire a songthaew for the day. A songthaew (two bench open-air taxi) will cost you about 2,000 baht for the day, including petrol (ask first!)
A minibus tour will cost around 1,100-1,200 baht with an English-speaking guide. The trip includes visits to the peak, two waterfalls, twin chedis, a royal development project, and a Karen village. The price also includes all entry fees. It is far cheaper to book direct with the tour operator rather than through a hotel or agent. The tour is from approx 08:30 to 16:30. All fees and lunch are included and you will be picked up and dropped off at your hotel.
It takes two to three hours to get there, and you will pay the entry fee for each person (not the driver, if it is a hire), and also the car entry fee. Make sure you book your planned itinerary with all potential stops before you hire the driver or they will charge you extra.
As you drive up the winding road to the top it will become steadily cooler. At the top you can walk around and check out the sights there. There is a shop for souvenirs and also for drinks and snacks (also toilets).
Why not continue your exploration of the North of Thailand even further by traveling the Mae Hong Son Loop.