First Floor

In the middle of the wide ring stood a single door. Above it floated the number 1, indicating the level Arthur had reached. Of course, the first floor is where he would start. The tower can only be challenged individually at the beginning. After the first twenty floors, parties can be formed. 

This was to ensure that even healers and other non-combat professions possess a certain strength to advance. Those with abilities unrelated to fighting would need to fend for themselves at one point, so it wasn't odd to see a healer that trained in a strengthening art. 

Arthur walked toward the door and touched it, asking to be transported to the first floor. If he can clear more floors, he could choose whatever floor he had been to. That was because there were giant floors that were shared among all the participants.