Have a long layover at Amsterdam Schiphol airport? Take the Fyra into the city!
The train ride to Amsterdam Central Station takes under 20 minutes and the roundtrip will cost you a mere €7. Trains leave every 10-15 minutes and the ride on the Fyra is fast and quite comfortable even for the exhausted traveller.
Amsterdam is a delightful city and is so much more than its Red Light District and pot smoking cafes if neither are your cup of tea. With how incredibly easy it is to get into the city, exploring it on your layover is an opportunity that shouldn't be skipped even if you only have a few hours to spend in it.
One word of advice though if travelling with a roller bag, leave this at the airport either in the free lockers in the lounges (in the KLM lounges they are usually to the side of the welcome desk) or the locker rentals in the terminal. The Old World charm of Amsterdam with its lovely cobblestones are fun to walk on but are no fun for roller bags.