Cologne Cathedral remains closed to tourists after terror warning. Church services are still possible. But in between, the landmark in Cologne will be closed to visitors due to the tense security situation. Normally, the cathedral is visited by more than 100,000 people from Christmas to New Year. The cathedral is one of the most popular tourist attractions in the city. The security authorities had received indications of a possible attack plan by an Islamist group on Cologne Cathedral and a church in Vienna. In Austria, four people were arrested during investigations against an Islamist network.