I found these huge cacti in a garden-center, the two on the right. The largest in the back was over 1.5 m in length! They were a little bit too expensive, so I thought maybe start from seed...
What species is this, and how long does it take before they are as large as these? And how to get them this big, is that possible as houseplant, or do you need a greenhouse for this?
Edit: I went back to the garden center, and found names on the labels! The two tall ones on the right are indeed South American cacti. They are called Trichocereus pasacana, a.k.a. Echinopsis atacamensis. So Echinopsis was a very good guess (see accepted answer). The two on the left were Pachycereus pringlei, just like the answer suggest!
The little one between the two tall ones on the right was sold, so I couldn't see what it was.