Yeah seems rather risky to be operating literally in the backyard of a major German submarine base. Six Type 212 subs are based in Eckernförde, one is actually on the marine tracker linked in the comments above [0] right now. If a submarine pops up there unannounced that's a diplomatic incident at least and with a naval base nearby the risk of discovery would be rather high.

[0] https://www.marinetraffic.com/en/ais/home/centerx:9.973/cent...