Daedalus? Labyrinth Mod 1.12.2/1.10.2 adds a new dimension for you to explore. To enter the labyrinth look for one of Daedalus? abandoned workshops in villages, they contain a portal.
Right-click the top block and it will open up the portal.
Going through a portal does not create a second portal in the other dimension. A portal closes again after some time and it is not fixed to a position on the other side. Going through a portal today might drop you off somewhere else than going through it tomorrow. If you plan to explore the labyrinth with friends make sure to enter the portal together so that you spawn as a group in the labyrinth.