Amsterdam Schiphol is the nearest airport, from there you can get a train to Utrecht which leaves every 15 minutes, and only takes 30 minutes.
On the day there is a shuttle bus from Utrecht Station to the festival with a return costing €5.
There is also a massive bicycle-parking area where you can lock your bike. A very popular choice for some!
To attend you must be 18 or over. Bring ID to ensure entry.