I had in an older version a magma bomb setup in the main corridoor.
Corridoor was 5 wide. Above it was the launch setup, with iron hatches. Above that, was the magma reservoir with another set of iron hatches.
The corridoor was like this
Hatches were setup like this:
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When lever was pulled, the 7 layers of magma landed on the tile, and spread around. Lower hatches could be closed, and storage reloaded from the magma chamber above. Or both hatches could be left open to flood the entire hallway with magma (I had bauxite floodgates at both ends as a safety feature).
On the outerend of this was a endless chasm with a rectractable bridge.I also had pressurized water directed to this corridoor. I could fill the corridoor at the pace of 15 tiles per cycle., and use the water to push all those wortless leather, silk and cloth stuff into the chasm.
The original idea was that there would be 14 layers of magma for each 15 tile set, proving a nice coverage. And since it is only 1 layer, it would evaporate fast.
However, experience proved that even at 1 layer the magma evaporated too slowly, So I needed two additional exits. But it was a good experience.
I was toying with idea of making a magma mist generator to burn people coming in, but haven't gotten around to that yet.