The Basement is where at least 3 of the challenges in Season 1 take place; those challenges are The Ungodly Machine Challenge, the Exorcism, and the Ring Toss Challenge.
Episode 2-The Ungodly Machine
Andrea and Lele are voted for this challenge; their partners are Justine and Eva, respectively. The objective is to send the machine in malfunction; the first one to do so frees their partner while the other one in the chamber is exposed to toxic gas, ending their life. If, in thirty minutes, neither of them are successful in sending the machine into malfunction, both participants would be exposed to toxic gas and a monster was to emerge. Eva is successful in sending it into malfunction, meaning Lele is saved. Andrea is exposed to toxic gas, which ends her life.
Episode 5-Did Someone Call For An Exorcist?
Sierra and Matt are voted to take on this challenge; Matt must follow the directions he is given while Sierra must hold onto the possessed woman and recite a prayer close to the Prayer of St. Michael, The Archangel. If Sierra lets go of the woman, she dies. Matt, unsure of how much time he has for the last step, neglects to read all of the last instruction. In the process, Sierra dies after Matt puts the rosary around her neck. Reading the note in full, he finds out that he had a choice; he could've either put the rosary on Sierra and killed her or he could've put the rosary on himself and died.
Episode 9-Wicked Hallucinations
Lele and Oli are chosen with their partners, respectively, being Joey and Eva. This challenge, which is in "the darkest part of Vincent's psyche" is the final hallucination they need to get through in order to free Vincent from his straitjacket. Unlike the other hallucinations, the consequence for failure is pain and death. Two of them must be selected, by vote, to sit in "the chair of a madman." Going into the basement, they discover two electric chairs or "learning chairs" and find out about Dr. Price, who had developed this to overcome hallucinations. Lele and Oli are strapped into the chairs, while Joey and Eva must throw metal rings to get them around the five electrical rods. Missed rings give their partner a little shock. The first to have three rings around any of their rods will complete the circuit and cure the partner's hallucinations. The guest who "failed to learn" would be given a severe shock which would end their life. If, in thirty minutes, neither of them had three rings around their rods, both of the chairs would short-circuit on their own, killing both guests. Eva is the first to get the rings around the rods, meaning Oli is saved while Lele is electrocuted to death.