I noticed there are 2-3 "spots" that I get a lot of feeling from. Btw I learned this over the past ~6 months and it took me a while to find the right toy, position etc. So be patient and try to not make ejaculation your goal, which can be very hard at first, especially for us men who have been used to orgasms that are coupled with ejaculation all our lives. (I enjoy being a man very much, but I'd love to be a woman for a day just to know how it feels for them )
First spot is the Anus itself, especially the inner ring of muscles, that feel very nice when slightly stretched or massaged (even though bigger toys and stretching can be a turn on too, i get the most feeling from smaller toys with just the right size). Then secondly, there is the prostate and walls just a few inches behind the opening. I have to tell you the prostate doesn't do a whole lot for me. Direct stimulation with fingers, even when my GF does it, doesn't bring any kind of special sensation for me. A dildo can feel nice there but it's hard to say if it's the prostate that is doing it or the just the nerves in the general area, anus/walls... Then lastly, there is the third spot and it's pretty much where the magic happens for me. I hit it perfectly with a ~5inch dildo so I'd say it's right at the end of the rectum, where the colon begins. Not sure what it actually is there but there seem to be a lot of nerve endings there in my body... (I've read something about flaps? Or could be the bladder?) It feels better if I'm completely relaxed so I start of with other things that feel nice (prostate area) and then take it deeper, while the other areas are still being stimulated ofc. It feels like waves of pleasure that build and build, that are so intense that i mostly forget about my penis and everything else at that point. That's what I describe as an anal orgasm for me because my heart starts racing like crazy and I forget everything around me - typical orgasm sensation. Btw best positions for me: riding the dildo or laying on my back. So far I don't ejaculate from that, at least not in the same way as with penile stimulation. There is an unusual amount of precum involved and there can also be semen (white) in there but nowhere near the same amount as a penis-orgasm-ejaculation. The upside is, that there can be multiple build-ups that are getting even more intense one after the other. It is very satisfying but it's not in the same way as a regular orgasm with penile stimulation. There I feel completely spent afterwards and all sexual thoughts and horniness are gone for a while. With an anal orgasm I keep that slight tingle while still being somewhat done. From what I've read in this forum and what my GF (we're mostly anal-only+sometimes clit) is telling me that's pretty much exactly the way anal-only orgasms feel for women when they don't touch their clit or vagina.
Of course I can also couple that with penile stimulation and then I get a crazy "final" orgasm with ejaculation. What I'm experimenting at the moment is how much or how little penile stimulation is needed for me to have ejaculation. I know it's possible to cum from anal only so we'll see. My GF and I didn't have the courage to go all the way with pegging so far, maybe that will add something as well?