Going to Bangkok - (DMK) airport and directly back to Vietnam.

At Dong Mueang Airport there is a Sleep Box. But it is outside the transit area. You cannot unlimited enter Thailand without a visa. Up to 3 times a year is safe.

An online visa platform suggested the visa-run without leaving the transit area.
But I read somewhere that this does not work, because the Vietnam immigration checks the entry stamp from the third country.

mix624 wrote:

I dont know if it would be worth taking a Taxi somewhere for a few hours and get back to the airport in the evening? I have never been to Thailand so thought I would ask.

Yes, it would be worth, and you might like BK so much that you won't return to Vietnam, the difference between Hanoi and BK is greater than Bucharest vs Helsinki.  Also, there are buses from DMK to the centre for about 35THB IIRC, no need for taxi...

mix624 wrote:

So my main question still is what they ask for when landing at the airport when no VISA is needed?

You mean, for visa on arrival? You'll need a ticket out of the country, 10 000THB worth of cash and proof of accomodation (just print out your hotel/apartment booking confirmation e-mail). With a stay this short, they might be lenient, though, or, who knows, maybe they'll get suspicious and be more strict...

Swedish people can enter Thailand for up to 30 days visa exempt, no fee, just breeze through.There is a good hotel in the airport called the Amari.It is linked to the airport by a walkway so no transport needed.

JOHNMELL wrote:

Swedish people can enter Thailand for up to 30 days visa exempt, no fee, just breeze through.

You're right, I thought the visa exemption applied only to a handful of countries, didn't bother to check... 

JOHNMELL wrote:

Swedish people can enter Thailand for up to 30 days visa exempt, no fee, just breeze through.There is a good hotel in the airport called the Amari.It is linked to the airport by a walkway so no transport needed.

Thanks JOHNMELL, that was the confirmation I needed, just to breeze through.

But I think I will not stay at the airport only without entering the country as AkaMaverick mentioned, I probably need that entry stamp.

Atomheart also mentioned that my short stay might make immigration suspicious and it might get problematic? Isnt a VISA border run a legitimate and understandable reason for Thailand immigration?

mix624 wrote:

Atomheart also mentioned that my short stay might make immigration suspicious and it might get problematic? Isnt a VISA border run a legitimate and understandable reason for Thailand immigration?

It was more like a joke, you should not expect any issues to my knowledge, especially if this is your first entry to TH.

I do the visa run every 3 months from Tan Son Nat (been doing it for years) entering at Don Muang & Suvarnabhumi. Fill out the entry form you get dished out on the plane. It will ask for various details incl Hotel, e mail address, telephone number. I have never ever been asked to show my return ticket, never been asked about how much money I have & never ever had them check the hotel I put on the form. Its a breeze as JOHNMELL said, no worries & its nice to see immigration officers smiling at the Thai entry points!!! & never ever been asked to give money!!
As for hotels, I have stayed at the Amari,  its ok & convenient but fairly expensive, but there are many cheaper options a short taxi drive away.

If you are doing the 3 months visa run (or 1 month after July) in my opinion going through Suvarnabhumi is the best option if you want to go down town!! 35 THB airport express to Makasan & all the attractions.