Has anyone encountered this?

I was experimenting with anal play the other day. It was my first time and I was trying to find my prostate (a.k.a. the male G-spot). So I put some lube and started loosening my external sphincter using my index finger.

Long story short, I was able to insert the whole length of the finger and suddenly I could feel some sort of small flaps/glands/protrusions up the rectum? I think it was far above the prostate already.

It was not painful. It was just there. I can only describe it as small with a texture similar to that of broccoli.

What is this? Please advise.