As a math teacher I love when anything makes sense in the world in relation to numbers. At our fist AirBnB destination the elevator showcased the Swedish sensibility: using the number line for the floors! If you think about it, this really does make sense - the "1st floor" implies the first floor above ground level so it should be represented by a "1". And anything below ground level is negative because you have to go down. If you want to know the true distance between floors, just subtract one from the next and it will always work out (even 1 - (-1) = 2 floors difference).
During that time we visited one of the best museums (and sites) in the world: The Vasa Museum. During a 17th century war between Sweden and Denmark a variety of sailing ships were commissioned to win the various battles: the Vasa was a beautiful example of one that, unfortunately, didn't make it out of port. As you can see from the picture here, the stern (rear) of the ship was so tall and so weighty that one side-ways gust of wind sent it to the bottom of the sea.
The story does not end there, however! 300 years later it was discovered and raised slowly, treated with a chemical glue-substance for 17 years to avert wood-splintering and cracking and now it is on display in all its glory. We spent 2 hours exploring the outer edges and reading about its history, its purpose, the raising, the life of a soldier at the time, and more. It was glorious.
There were many more amazing things to do in Stockholm but not enough space to write about them. I highly recommend you visit.