I've added a curve spiral with Curve -> Curve Spirals -> Spheric (This might require an add on to be enabled like "more curves"). I'd like to have a second spiral that is parallel to the first to create a spiral track that a vehicle like a roller coaster might ride on.
This is proving to be quite difficult however, since you can't just duplicate and move or scale it since the ends don't line up top and bottom. I'm thinking there's a formula that I need to use to generate the two spirals, perhaps using an XYZ math object or similar.
And the bottom (which is not at all aligned):
As a side issue, the spiral shape also seems to be beveling in a strange way. The bevel object is just a circle (curve) but it deforms into an oval shape that changes axis the whole way down.