Night train from Aachen to Salzburg
There currently is one option to travel by night train from Aachen (Germany) to Salzburg (Austria), taking approximately 11 hours: Namely the NJ 40425 operated by ÖBB.
The Austrian Federal Railways (ÖBB) operate the Nightjet and Euronight trains (the latter together with other national railway agencies). ÖBB night trains typically feature three types of carriages: seats, couchettes, and sleepers. While seats are only for the bravest, couchettes and sleepers offer a more comfortable journey. Couchettes accommodate up to six people, while sleepers are private compartments for one to three people. They sometimes include a private bathroom or even a shower, sometimes only a sink.