Those who come to Sri Lanka, which requires a visa. It can be up to 4 weeks eta.gov.lk apply online on the and pay for a stay. Or you can buy it at the airport in Sri Lanka. It will cost but about 10 euros more per person.
Originally Posted by ETA Sri Lanka page:
The ETA is initially limited to 30 days from the date of arrival and can be extended up to six months.
Please note, if you applied for the visa on the website that one enters the correct passport number! Also, the letter at the beginning you have to. Otherwise you have problems at the airport.
However, one can also apply the same from his home country for a visa! This is usually cheaper and you get it the same for a long time, saving you the drive to Colombo and the day that you need, because you have to wait meaningless until you get the stamp.