Do we need to show passports or driver's license as ID cards when entering museums and Cathedrals in Spain? Would a photocopy of the passport work instead of the real document?

Thanks

Assuming you are paying full price not in my experience. OTOH I think Spain requires you to travel with ID.

To enter museums or cathedrales, no, but the law is you must carry ID with you. vinonobile is probably right - if you want to rent a gismo at a museum or elsewhere they'll probably ask for your ID.

Not sure if that is still the case, but some years ago, I had to show ID for credit card purchases in Spain because my credit card had a bug and I could not do real chip + PIN. So you may need to carry your passport with you anyway?

I just returned from Spain a couple of weeks ago. At the cathedral in Toledo, you have to leave ID, driver's license or passport, to get the audio guide, which is included in the entry price. You get it back when you turn the audio guide back in. You get the ticket across the street from the entrance.

That was the only place I had to do that, but I think it's also the only place I got the guide.

NO.
Unless you qualify for a reduction (pensioners, students, children).

In certain monuments (Toledo cathedral, Alhambra), when renting the audio guide, you'll be asked to leave an i.d. as collateral until the audio guide is returned.
In museums, if you ask for reduced price admission, like those that jannie mentions, you'll need to show an i.d. as proof of age.

At the Museo Naval in Madrid, you'll need to show your passport or driver's license, as danon states, because the museum is housed in the Spanish Armada's Naval Headquarters.

Lots of places ask you to leave something of value (ID or credit card) when you rent an audioguide (in any country). In fact, I think every place I've been does that, they need to make sure you return it. I'm surprised that cathedral would not take a credit card, but only something that is ID. They don't care about your ID, really, just want to make sure you come back. I never leave my passport at such places, just makes me nervous if it got misplaced. I leave my driver's license usually.

"NO.
Unless you qualify for a reduction (pensioners ...)."

Damn, they didn't ask me. I must look older than I think