Hi! We will be staying in Montmatre whilst in Paris next week, and one of the days we will be taking a night bike tour of paris which ends with a seine cruise. The alarming part is that it will end somewhere around 11.30pm and after reading many reviews on safety in the nights i'm a little nervous as we wiil need to find our way back from somewhere near seine/eiffel (i'm assuming) to Montmatre. What's the best way to travel back safe? Would appreciate any tips!

Get a taxi. Much less stressful than dealing with the metro late at night.

Taxi

11:30 is not that late.

There is nothing to be alarmed about. Paris is as safe a big city
as you'll find.

11:30 is NOT late. But I would do a cab just since Metro doesn't run frequently at that hour. (We have walked home from after dinner movies, film festivals and clubs often at 1 or 2 am with no problem at all.)