You don't have to book your tour in advance, just show up at the meeting point. Notice that due to coronavirus, there can be max 8 people per tour.
All tours are free with an AarhusCARD. With an AarhusCARD you get free entrance to more than 40 museums and attractions, free parking at Navitas and free transport with bus and light rail in Aarhus and the entire Central Denmark region.
Domkirkens hovedindgang på Store Torv
8000 Aarhus C
50 DKK - 100 DKK