Without modern electronics, how could you determine your longitude, latitude, and altitude while lost deep underground?

Altitude (or depth) can be measured with a barometer.

Latitude is doable, but tricky. Two methods come to mind, but they require staying on one spot for rather a long time to make accurate measurements.

The first option is to use a Foucault pendulum. The rate of precession of such a pendulum is directly related to latitude; the pendulum conveniently serves as its own timekeeping device, so you don't even need a pocket watch to go with it. A projector and a single-sheet conversion table would be sufficient. You just have to hang around in one spot long enough to get an accurate measure of the precession rate, which would take several hours at least, and while it could be packed down quite compactly for transport, the device would be rather tricky to set up.

The second option is to use a gyroscope. //

Longitude is much harder. //

With a combination of pocket watch and really good gyrocompass, however, you can do better. To make this work, you will need an extremely accurate gyrocompass set rotating at a known position (say, when you enter the dungeon system) exactly perpendicular to the planetary axis. If you were to stay in one place, it would appear to rotate at a known rate as the planet spins, making one full rotation every day, so you can compare its actual rotation with that predicted by your pocket watch. If you stay in one spot, they will match exactly--but if you move east or west, they won't. The difference in the actual position of your gyrocompass at any point from that predicted by the pocket watch will indicate transport around the planet's axis farther or lesser than would be accomplished by the planet's own rotation--and thus, indicates how far you have traveled across the planet yourself.