If you're in the swamp, find a crypt, and simply build a hut on _top_ of it.

Making a crafting bench, and place it on the back side of the crypt (opposite the door that leads inside). Jump on the bench, then you can jump onto the top of the crypt (because the back side slopes down)

Place some floors, walls, roof, etc. Make a little shack on top. You want it completely enclosed, due to the wraiths that fly around the swamp. Place a portal inside. On the front side start putting some stairs down to the doorway. Run around, dismantle the bench, and move it upstairs.

if you're really obsessive, it's actually possible to build walls around the front of the crypt, completely blocking it off from the outside. You can portal in, run down the stairs into the crypt and back up to the shack. When you're cold and tired from mining the crypt, you can go kick back in the shack upstairs, safe and sound.

When I had stacks of iron mined out, I'd start hauling it to a crypt/shack near the water. Best is when you literally have one IN the water or right next to it, and you can build a boat dock right there. I had all the iron from about 6 crypts all moved to one near the water before I even started to haul it back on my ship. I lucked out and found a cluster of crypts literally within sight of each other.

i did this for every single bloody crypt I mined out. I left the portals in place, and gave them unique names (and put that exact text as a tag on the map).

Turned out later on that some of these portals in the swamp happened to be near stuff that was worth farming, like the fire vents that spawn surtlings. I'd portal into the swamp to gather plants, seeds, farm leeches, draugr intestines, etc.