Angkor is very accessible from Bangkok, loads of cheap places to stay as very popular with backpackers, loads of cheap street and restuarant food and $1 beers or $2 cocktails. Tuk Tuks can take you to the temples, there was a stream of them when we went to see sunrise at 4.30am...you can basically negotiate the fare, my guess would be around $10 return, they will take 4 people. We did a great cycle ride too around the temples, we had transport but I'm sure a guide would take you from Siem Reap centre to some of the closer ones to pedal around
Phnom Penh is very interesting (and depressing) with the Khmer Rouge history, and about an hour flight from Siem Reap
Get Trailfinders or similar to price up flights for you

But as above, it will be stupid hot (100+) and humid and possibly wet in July, Christmas better
I have to say my trip to Vietnam and Cambodia was probably the best holiday I've ever had

I've 'done' a lot of the US, the Canadian Rockies, I've been on a luxury safari in Tanzania (for a wedding), I've been to Thailand...the only downside for me with Asia is the very long flights (as a nervous flier

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