Public transport is pretty good in the Netherlands. The website 9292.nl can help you plan your trip. Basically, you need to find the train to Venlo. Then catch Bus 377 to Castle de Berckt in Baarlo. The bus platform at the train station is where your weekend starts as it is unlikely that you are the only one on that Thursday afternoon trying to get to the Castle. We can already sing hash songs on the bus if the driver is in a good mood. From the De Berckt bus stop it is a short walk to the Castle. The bus ride takes just 17 minutes, but the frequency is only once an hour in August. Ask the bus driver to tell you where to get out.
Train rides are a pleasure. Bring your own picnic with beer or wine and enjoy the trip. Bringing booze could come in especially handy if you arrive at the Castle before 16.00 when the bars open.
Be smart and take into account the time you need to get to the venue from these airports on Thursday as well as the time needed to get back to the airport on Sunday. Arriving late on the Thursday evening and leaving before breakfast on Sunday is not ideal. Consider booking extra nights before and/or after the event. Ryanair is cheap, but connections suck most of the time.
Schiphol Airport Amsterdam
Schiphol is fully integrated with a main train station. Direct trains to Venlo depart every 30 minutes - then it is 2 hours + 10 minutes to Venlo. In Venlo, you take the bus to the Castle.
It is well connected to Venlo. Buses depart every 30 minutes for a 20-minute ride to Eindhoven Central Train Station. Direct trains to Venlo depart every 30 minutes - then it is 40 minutes to Venlo. In Venlo, you take the bus to the Castle.
Maastricht - Aachen Airport - It says Aachen but it is Maastricht in the Netherlands
Bus 30 departs every 30 minutes to bring you from the terminal to Maastricht Train Station. From there you take trains for 1 hour to Venlo. In Venlo, you take the bus to the Castle.
Ryanair - Dusseldorf - Brings you to Weeze Airport, which is not Dusseldorf at all.
It is not far away, but public transport sucks. Book a taxi or shuttle from this airport. Try to arrange that they bring you to the venue instead of dropping you off at the Venlo Train Station (Venlo Train Station is the default destination for airport shuttles).
Dusseldorf Airport - Fair warning, this is not the airport Ryanair uses. Ryanair uses Weeze Airport.
It is not far away, but public transport sucks. Perhaps best to book a taxi or airport shuttle. Try to arrange that they bring you to the venue instead of dropping you off at the Venlo Train Station (Venlo Train Station is the default destination for airport shuttles).