New objective: Return to Town. Head instantly right, dodging the laser and use the tube to return to town.
Speak to Dorothy again.
New objective: Explore Vectron.
Continue, as ever, to dig downwards.
Watch out for the partial blocks like the one above your character in this screen - they regenerate shortly after you dig through. It's best not to go through any of these when building downwards, as you probably won't be able to come back through them - go around where possible.
Continue downwards as normal. Magnets work in a similar way to the heavier blocks previously although they can go up as well as down and also side to side. The direction is made clear by the way it is facing.
You will reach a point where you can progress no further due to a laser beam - head central to cave one.