For various activities at the Mega in Vienna, you need to book a time slot.
For example, for a guided tour of Parliament:
Find out about the impressive architecture, the eventful history and the extensive restoration of this unique building
Some of the dates are already quite fully booked. Secure your preferred date now by making a booking. The guided tours are available in German and English.
Book a tour: https://www.geow4.at/fuehrungen-parlament/