The room consists of 3 cacti and a sign in the middle that says the next art club meeting is on October 10th at 8 pm. A sign can be found in the black space next to the hallway in MTT Resort advertising the room.
This room is inaccessible by normal means on the Genocide Route due to the second floor being blocked off by a force field.
A secret boss, So Sorry, can be encountered here. To do so, the game must be launched while the player's computer clock is set for October 10th, 8 P.M. Additionally, Hotland must have been cleared up to the MTT Resort. If these conditions are met, reading the sign will cause So Sorry to run into the protagonist, initiating his encounter.
The Nintendo Switch version of the game has the sign removed the 8 P.M. part, allowing Nintendo Switch users to face So Sorry all day instead of 8 P.M. 
- ↑ "Today's the day you can go to the Art Club on Hotland 2F and have a special meeting. That's 8PM (your time). On the Switch version you can meet all day though!!" - Toby Fox. October 10, 2018. - Twitter