Long week long interview with multiple round of discussion with group leaders and an initial asessment, which happens first and one needs to pass to qualify for next rounds. Only then you interact with group leaders.

The process is exhausting, as you have to interview with multiple people and more than once if you're shortlisted for a project. Initial Assessment is nerve-wrecking but almost everyone passes it. I didn't really like the fact that you had no idea what kind of projects were available before going to Heidelberg. However, overall it was interesting, they cover for everything and you meet tons of interesting people.