This monastery is on the east side of Plaza de Oriente, close to Puerta del Sol. I saw a few foreigners queuing outside, and they followed in line. I checked on my mobile phone and found that this was the monastery I saw in a travel blog. It's still pretty inside, and there are many authentic ones. After standing in line for a while, I realized that the door opened at 10 o'clock and I had to follow the group. It was only 9:30 and I had to wait for half an hour. I had to catch a plane at one o'clock in the afternoon, so I had to give up. When I left, two old foreigners told me that the door would be opened soon, and I was speechless. The foreign grandfather and aunt came really early.
This is also a more famous attraction, if it is suitable for in-depth tour, come and go.