Hello Spinlanders. Do you want to play a game?

Turns out a jigsaw and a thick aluminium can are a nightmarish combination (although not as nightmarish as the title might suggest).

The void that is now visible was the liquid
nitrogen reservoir

The aperture visible directly below the liquid nitrogen
port allowed nitrogen gas to vent during weekly fills. 
Liquid nitrogen was fed into the reservoir through a
similar aperture on the other side.

After our quick progress yesterday through the outer stainless steel layer, it was a real struggle to cut a window into the liquid nitrogen vessel.  This vessel is constructed from a sheet of aluminium ca. 4-5mm thick, and getting through it with the jigsaw was hard going!

We have now arrived at a point that differs somewhat from the records we have available and it's not entirely clear how best to proceed.  But fortune favours the bold, so forward we go...