This was by far my most unpleasant experience with Air Bnb - ever. First of all, the flat is NOT located in Södermalm, but in Gamla Stan, which is a different part / island of Stockholm. However, that is a detail in comparison to what happened the first night of our stay.
After having checked in and left our bags at the flat we went out to meet a friend. We returned in the evening to find the door closed, unable to open it with the key code provided by the host. It was clear to us that someone had locked the front door from the inside. We tried every possible action to open the door, besides wrecking it. We did not want to cause any damage trying to get in, so the only thing to do was to face the fact that we were unable to access the flat with our belongings in it, and find a place to spend the night. As the host provided no phone number or did not respond to my urgent messages via the Air Bnb app we had not other choice but to return in the morning and hope we could get in.
The next day at 9:30 am I finally received an answer from a co-host, stating that the flat is always accessible and that I should just 'lift the door handle upwards'. We proceeded back to the flat, were we tried out the advice given. Needless to say it was bogus advice. The door handle does not even move up a tiny bit. Luckily the door had been unlocked from the inside so we were able to get in. We then noticed that indeed, there was night lock on the inside. We proceeded to film everything and sent Air Bnb a detailed report, as well as another message to the host, to which until this day we received no reply. We also decided to not spend another night at the flat, and left with our bags.
Air Bnb has reviewed the video and issued a near 100% refund, to their credit. The only communication we received from the host afterwards was a standard 'rules for checkout' message. As if nothing ever happened.
It is a very unpleasant experience to be locked out of your place for the night, with everything you brought locked inside, including a laptop and other valuable belongings. So my advice would be: stay away. This host does not care.