By air:
Unfortunately Switzerland has only four major airports in Zurich, Basel, Geneva and Lugano. Your best choice is Zurich and Basel.
You can find budget flights here:
http://www.whichbudget.com/budget-airlines-en.html#to15

By train:
In 99% of the cases you will have to go through Lucerne, from where there are fast trains(20min) to Sarnen every hour from 05.30 until 00.30. There are also slower trains(30min) every half hour.
From the train station it is a short walk and signs will be posted.
For connections from Europe please check:
http://www.sbb.ch/en/

By car:
For northern departures Lucerne is also your prime destination, from where there is a highway directly to the camp.
For southern starting points Milano and the Gothart Tunnel is the way to go.
In both cases please take the Sarnen Süd exit no.35 from where you can see the camp and directions will be posted.
For detailed route information please check:
http://www.uk.map24.com/