A profuse bloomer.
Argentine Giant (Echinopsis candicans)
This is a photo of "Echinopsis candicans".
Your blooms are too big and the sepals are red.
Your stems are too thick and the spines are to big/long to be Echinopsis imperialis.
Take a look at this photo of Echinopsis x imperialis.
And here of Echinopsis candicans....Here the sepals are red, the flower is bigger and the stems are thicker and the spines are bigger (like yours)
Here's two more examples of Echinopsis candicans in this thread, photos by Judyb & azrobin
Would you like to have this photo and your other photos of this plant switched over to the right page in the PlantFiles?