Koreshans believed the earth is hollow and we live on the inside surface. One of the most interesting things about them is looking at the ways they rationalized their beliefs and refuted the considerable evidence that contradicted what they had been taught. There's a fair bit of this stuff preserved at the site.
They did have a lot of progressive ideas, notably universal suffrage for women in the 1800s (!). Indeed, the governing body of the sect was all female, even if the leader/founder was male. They did make a good start on building their New Jerusalem, managing build and operate a sawmill, printing facility, school, boat works, cement works, bakery, laundry, orchestra, and electrical generation and power to their enterprises and residences. Thomas Edison visited them to see their electric installations and confered with their engineers.
In spite of their progressive social and technical achievements, they had many of the trappings that most of us would recognize as a cult. It would be fair to draw parallels to the Rajneesh cult in Oregon a few decades ago.