Originally Posted by
Showbizguru
Er, any advice on which part of the mainland within perhaps a day's journey from BKK ?
Any point in Thailand is within about an hour's flight or an overnight train journey from Bangkok.
And mainland v islands in December ?
I also have absolutely no knowledge of Thailand whatsoever.
Sure looks like it. Please start by consulting a map, and you'll find that your question is absurd, as the mainland has the same climate and same appearance as any islands next to that part of the mainland.
A slightly more sensible division of the country:
Now, tell us what kind of things you're interested in, and we can start suggesting where you might want to go.