All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
We will give the same answer that we gave in previous fataawa, that it is impermissible to go to such gyms except for a sharee'ah-acceptable purpose. Please refer to fatwa 90256. We have highlighted alternatives to going to the gym in fatwa 91237.
The fact that the gym is large does not make it permissible to go there unless the Muslim can work out in a place where he cannot see any prohibitions being committed therein. In that case, he is permitted to go. The Hanbali book Ar-Rawdh Al-Murbi' says about answering the invitation to a wedding banquet, “If the person invited to a banquet knew of a prohibited act being committed there but he did not hear or see it, then he is given the choice either to stay and eat his meal or leave given the absence of the obligation to forbid the prohibitions in such a case (because he does not hear or see them)...”
However, if he actually sees prohibited acts being committed, then he is not permitted to stay. The Muslim may lower his gaze once but fail to lower it a hundred times, thus his heart becomes a target for Satan's poisonous arrows, luring him into fitnah (temptations and immorality). Verily, nothing is as valuable as keeping one's religiosity safe.
Allaah knows best.