I don't think it was portable without destroying what you built.

It was an interactive portal (it may have been a stone ) that when you placed it a big island formed up above you and you could port up to it in the sky through the stone (you fly up like you bounced), you land on a little dock where there's a portal/stone to get back down and then there was a huge flat green building area to play with. It was visible from the ground- not an instance.

I went back to the seed I originally had it on with the same player and the structures were there but no land - it just slowly disintegrated and everything fell to the ground in pieces...including me.. lol

I thought it was a part of home and hearth since it wasn't mentioned in any mods I dl'ed - it was just there when I was messing with stuff in the same crafting list as the normal portals. It's not a HUGE deal, plenty of land to build on in the orig game but I HATE terraforming and was very happy with the find... now I'm bummed since I was looking forward to building on it some more and seeing what I could come up with.