This e-ticket expires after 3 months of buying. After buying a ticket you will get an invoice on your email and you need to show that invoice at the entrance of the museum. If you are a student or pensioner and want a discounted price for students or pensioners, you will need to buy ticket on the site. There is also the possibility of buying tickets offline on-site in the Museum of Hangovers. It gives you unforgettable experience ;)