Within the universe of Deep-Sea Prisoner's works, there are multiple unnamed human worlds. This was first strongly implied in Seaside Dispatches 2 and thereafter confirmed by DSP during a live stream in September of 2020. 
Human World A
This is a placeholder name for the world that Yonaka Kuraui originates from. It would be safe to assume the locations of this world are - generally speaking - the same as our world as we do get to see glances thanks to Mogeko Castle and a calendar image that supports this idea.
Yaboshi High School
- Tomoe Yahata, Imika Yuhjima, Nataka Kurokawa, and Ringo Ame all attend this school. Ren Yokoshima teaches here. Eruko used to attend this school before moving homes. One unnamed character, currently nicknamed Dead Inside Boy, might also attend this school as he has been drawn together with Ren Yokoshima.
Human World B
This is a placeholder name for the world that Victor Flankenstein used to live in before it was destroyed by Fumus. A few minimal glimpses of this world were shown in Seaside Dispatches 2. It seems this world had 19th century technology.
Other human-related locations have also been shown in DSP's works that have yet to be confirmed to belong to specific worlds.
- Azemiti Toru, Kisaragi Alice, and Utareduyoi Tsubaki all attend the same school. Both Shinohara Souichirou, as well as another unnamed character, are teachers there. Two other currently unnamed character nicknamed Skull Girl and Moge-san also wear this school's uniform, hinting at them being or having been students here.
- Mogeko Castle - Yonaka ends her journey by returning to Human World A.
- "Dying Tomorrow" - The story takes place in a human world, specifically the school that Tsubaki attends.