WIY:
The Tziz Eliezer Vol 14 Siman 91 deals with permissibility of visiting a mosque. He quotes the Ran in Sanhedrin (daf 61) who writes “and the crazy one of the Yishmaelim, even though they don’t mistakenly call him a God, since they bow down to him in the manner of bowing to a God, it is to be considered as Avoda Zarah, and all the laws and prohibitions of Avoda Zarah pertain to it. For they don’t bow down out of respect to the dead, rather as in the manner of worshiping a God”. The Tziz Eliezer on the basis of this Ran, concludes that one shouldn’t enter or visit a Mosque.