An Echinopsis, of which there are numerous kinds. It will likely bloom more for you in future years. Give a lot of sun in the spring and summer, keep it cool and dry in the winter.

I would say it's some species of Trichocereus (spachianus, perhaps?).

Was it fragrant? It's very beautiful - congrats!

-Chris

I thought the fragrance was similar to an oriental lily. The petals were of a similar texture of a peony.