We are trying to find the coolest (20-25 degrees) place to visit in June, within a four hour flight radius of Thailand. Any suggestions? Or does such a place not exist?
Thanks in advance,

Llasa looks good and if there were direct flights (which I doubt - yours to research) it would have to be in the 4-5 hour bracket. There are (were?)definitely direct flights to Calcutta - and from there to Darjeeling perhaps?

Or Kathmandhu - or maybe not at the moment.

Is that Celsius or Fahrenheit? 25C is about 78F, which is not really cool, but I guess compared Thailand it is. I will assume you mean Celsius:

Bhutan
Simla hill station in India
Highland parts of Malaysia in the interior
Highland parts of Vietnam in the interior
Seoul, South Korea and other parts of Korea
The Baguio rice terrace areas in the Philippines
Many parts of northern and interior China, esp Kunming
Northern parts of Japan like Hokkaido (may not meet your 4 hour limit)

The problem you will have in some of these places is that June is part of the rainy season, esp Baguio in the Philippines.

Thanks for all the suggestions. I guess I should have stayed more in the 20 degrees celsius range, and yes compared to the 38 degrees in Bangkok it would seem really cool..
We may have narrowed down to Malaysian highlands though Simla or Ooty may do fine.

Ooty