Travelers can easily take the public air-conditioned bus at the Northern Bus Terminal in Bangkok to Aranyapathet. Bus fee is at 160 Baht for air-con and half price for non-A/C. Taking the train from Central Railway Station of Bangkok called "Hualumpong" is not a bad idea with two departures at 05:50 a.m. and 01:00 p.m. and arrive at 12:00 and 06:00 p.m., respectively. Only 3rd class and non-A/C trains running this route at the fare of 48 Baht. Some travel agents on Khaosan Road that are specialized on backpackers do offer this transport service by van at the cost of around 250-450 Baht.
From the Bus and Train Station in Aranyaprathet, the Poipet border is roughly 6 kilometers away. You can take the rickshaw to the border (or in Thai called Tuk-Tuk) at around 40-100 Baht depending upon your bargaining power. No fix rates!
The scenario of the Poipet border is a bustling market where the Thais and the Cambodians of the two sides trade with one another. From Poipet, you can either get to Siemreap or to Phnompenh.
Cambodia visa processing here is rather easy. The foreign visitors just fill in the visa application form with 1 Passport-size photo. Show your Passport and pay USD 20 or 1,000 Baht for visa fee to the Cambodian Immigration officials. That's all the process needed to be done.
The Poipet border is open from 07:30 a.m. to 17:00 p.m., and foreign tourists can obtain the visa here. A slight warning is that you might be asked for some sorts of International Vaccination Certificate by the local immigration officials. It is only their attempt to make some extra money as there is no such requirement. Some travelers had reported that the fine imposed ranges from USD5-50. This is not legitimate, of course. If you insisted not to pay, generally the officials do not make any hassle further. In case you are quite afraid, pass the immigration with the other tourists so that you won't be alone, or if you want to compromise, some small dollar notes should be more than adequate, though not recommended.
After passing through the Immigration station, you can easily spot two casinos that host the Thai gamblers who travel to Poipet for legal gambling in Cambodia (illegal in Thailand). The good hotels actually the guesthouses in Poipet are mostly full in advance as they are pre-booked for these gambling group tours from Thailand. It is not a good idea to cross the border in the late afternoon to find yourself stuck there. Overnight at a decent hotel in Aranyaprathet at the Thai side is much better off and cross the border next morning or around noon.
In Poipet, the vehicles are rare to be seen. Taxi is run by private two-wheeled motorcyclist. There is a bus station near the crossing point, but it is vacant. Many wagons, full of goods and products, are pulled or pushed by several dusty Cambodians. Food and drink stalls can be seen on the two sides of the street.
Travel to Siemreap from Poipet is more or less a rough and adventurous trails, not suitable for those who seek comfort. On the Cambodian side, there are share taxi or pickup trucks that will ride you to Siem Reap where the impressive Angkor Wat and other Khmer temples are housed. The road condition is very poor, dusty, unpaved, and even worst in rainy season when the road becomes muddy with a lot of potholes. In some instances, local military guards may block the road to ask for illegitimate passing fees from travelers. If you are lucky, it takes around 10-12 hours for 150 km journey with an opportunity to cross some of the most exciting (dangerous) bridges that you never experience before. The transport fee one-way to Siemreap from Poipet starts from 100 Baht up.
The road condition between Poipet and Phnompenh is better than the one to Siemreap. General traveling time on this route takes around 8 hours in summer and nearly double in rainy season.
General Tips and Advice:
1) Try to be selective on the type of vehicles – recommend pickups, since the unpaved road is rough. If your vehicle breaks down along the way, it is likely that you will have to pay a much higher price for another vehicle that passes by to drop you off in Siemreap, generally at 2-digits US Dollar figure. No free ride on this route!
2) Aranyapathet-Poipet Border is the place where you can turn in and out and get another entry or 30 days. There is no Thai Consulate here, but rather a small Immigration post. If you wish to enter Cambodia through Poipet to travel around Cambodia and then leave at the same crossing point, be sure that your Thai visa has not been expired, or you will be given 30 days… otherwise you will have to make a double painful trip, either back to Siemreap for taking a direct flight out or even further to Phnompenh to get a new re-entry Thai visa. Its counterpart at Koh Kong border gives 30-days Thai Visa
3) Safety? – Though there are many instances of travelers being rip-off by the locals in the area, it may be unavoidable. Anyhow, most of them are at a bearable cost. Practice your bargaining skill is the only advice! Recently there is no report on travelers being physically harm or endangered, so it is likely to be at individual risk.