these are the old unnamed tunnels under desertopia. they were constructed to connect the first two netherportals i created. the tunnels are shallow, convoluted, and even turn back on themselves:
the entrance of the tunnels are in a backroom at the old desertopian house. they snake through underground, where a small mushroom farm and portal is located. then, they intersect with the quarry underneath desertopia before joining reaching the basement of the second desertopian house. after that, there is a single staircase up to the surface at the rock basin in desertopia and then stretch north for a few hundred blocks, reaching the nether portal, which still stands today.