You have to go to the Nepal Tourism Board at Bhrikuti Mandap.
You will need:
- copy of your passport
- 2 passport sized photos
- 4000 rupees in cash
There is a cash machine directly at the building to take out money if necessary.
The format of the photos do not matter.
Do not worry about the politeness of the people working there. They are clearly frustrated as hell and will not do the slightest effort to look at you.
You will have to fill in a form with the formalities of your hiking route and the length of stay. This does not have to be accurate, since everybody knows people change all the time.
Take the most extended hike and the maximum length of stay (one month) to give yourself more breathing space. You can exceed your stay very easily by not checking out or in any more.
Hu? What’s about the checking stuff?
Well, with your trekking permit you’ll have to go to designated check points where ACAP officers will ask you some questions and write your details inside their register. This controls the amount of people between the check points in case of natural disasters or to track you down more easily in case you get lost. The system needs some improvement, though, since - as the good student as I am - I wanted to check in asap, but the offices seemed to be closed all the time (I’m an early riser). So, it was not until Manang that I checked in for the first time, leaving me legally 6 extra days of trekking fun.
As I said before, you can easily exceed your permit by simply avoiding the check points if you are sure you’ll not get lost.