Two churches in Cologne. Alt St Alban has no online ticket listed; Cologne Cathedral has 4 tickets and tours to book. The table and the two notes below put them side by side; the full pages have what to see, the ticket and the timing for each.
There is nothing to buy: the church is a roofless ruin kept as a war memorial, open to the sky and enclosed by a low railing, and it can be looked into at any hour from the courtyard beside the Guerzenich concert hall in the middle of Cologne. No ticket, no opening times, no guide. Walking tours of the old town pass it and usually stop for a minute; those cost a moderate amount and cover a dozen sites.
The cathedral is free to enter and there is no ticket for the nave, which surprises visitors to Germany's most visited landmark. Three things are paid for separately and cheaply: the tower climb, the treasury and, on some days, the guided tour that goes behind the high altar. The tower is the one to take: 533 steps up a spiral staircase in the south tower, past the bell chamber with the 24-tonne St Peter's Bell, the largest free-swinging bell in the world, to a platform at 97 metres.