Originally Posted by Colonel Mustard
So you have just over a month to travel around? That isn't a lot of time for "Thailand, Vietnam AND a bit of Cambodia." I think you should choose Thailand or Vietnam. Thought about Laos? It's very lovely.
The only railways are the goods trains from Phnom Penh to the port of Kamping Som (Sihanoukville) and the Bamboo Railway around Battambong. Nothing out of Siem Reap. But...
There are some boats that can offer a nice river journey south from Siem Reap to Battambong, among other places. The region just south of SR is the Tonle Sap lake. Lots of river travelling available around there.
Close :) Bangkok is west from Poipet and north will take you up around Issan and up to Udon Thani, which is a lovely area.
Siem Reap is vey close to Laos. You can cross the border into Laos and visit a very beautilful area called Tsee Phan Don (4,000 islands).
Other than that, lovinarick is right and mostly in Cambodia you'll be travelling by bus from SR and I suggest you choose between Thailand and Vietnam.
If you want to travel to from SR to Chiang Mai, you'll need to bus across to Poipet (around 3+ hours), cross the border (30mins - 1 hour), train/bus to Bangkok (4-7 hours (I recommend train for the experience and it costs less than $2)), then another train up to Chiang Mai (12+ hours). I would strongly recommend that if you get the choice, you overnight on the Thai side of the border in Aranya Prathet as Poipet is a shithole. Some companies offer some all-inclusive tickets, but will be a bit more expensive and mean that you don't have to overnight (as one bus will be overnight), but it is also easier (and therefore less adventurous) for you.
1 month is plenty to see Laos, Cambodia and northern Thailand. But u will need to fly some places
divide it up,
10 days laos, ( luang Prabang, Phonsvan, Vientaine)
10 days northern Thailand ( Chaing Mai, Chiang Rai, Ma Hong Son)
10 days Cambodia (SR ( give urselve at least 4 days/nights there) an PP)
There is NO RR from shv to PP although they are rebuilding the RR between Battambang and PP for goods.
I don't call the 5 kms Bamboo RR trip a RR
SR to Laos?? only way is via Stung Treng an that will deliver you to south Laos, ( 4,000 islands is indeed nice) easier to exit north to Surin via the border at Osmach and than cross via Thailand
SR to Chiang Mai, you'll need to bus across to Poipet (around 3+ hours), cross the border (30mins - 1 hour), train/bus to Bangkok (4-7 hours (I recommend train for the experience and it costs less than $2))
Sr to Poipet is 2-2/12 hours by bus or Taxi
Train Aran to Bangkok is 5 1/2 hours and cost 59 baht
Better, quicker and most likely cheaper ( when u add in taxis, trains, overnight accommodations and food along the way) from SR to Chaing Mai is to fly
If ur really set on train /bus than head from SR towards Poi Pet an take the road up toward Surn. From there its a 1 day bus to Ventaine laos, there travel by bus to Phonsavan-Luang Prabang- Luang Namtha- Chaing kong where u re-enter Thailand and than head south to Chiang Mai by bus
U get 15 days visa exempt via land borders for Thailand
and it will cost u $35 us for a laos visa and $20 for ur Cambodian visa
It would be very difficult to combine Vietnam with a trip to Chaing Mai without flying in that time frame u have