It's not allowed. They are everywhere. Some cathedrals are huge. Some serve primarily as regularly worshipping congregations. Others are essentially museums and are visited mostly by out-of towners.
Some cathedrals are well-kept.
Others are in disrepair. Most are cold and have leaky roofs. Some collect an admission fee, some a donation, and some are free. But just when it seemed to us that European church buildings are only relics of the past, we happened, on a Friday evening, by the Cathedral in Verona, Italy. Young people were overflowing this huge church.