Another thought on spoons:
1 US tablespoon = 15 mL (thanks wikipedia)
1000 L = 1 cubic meter; 1 L = 1000 mL
So a cubic meter of dirt is 66,667 tablespoons.
Digging at one spoonful per second (assuming the dirt carries itself off somewhere), that's about 18 hours of digging per meter - with a narrow tunnel that a human in plate armor would have to wiggle through.
Also, I would think that without the aid of a level, you could burrow slightly upwards or downwards and so wind up falling through onto monsters, or tunneling under monsters and bringing them down on you (after a few weeks of excavation).
Did the Spade of Colossal Excavation make it to 3E?