  Presented here are first tests of a Gaseous Photomultiplier based on a
cascade of Thick GEM structures intended for gamma-ray position reconstruction
in liquid Argon. The detector has a MgF$_2$ window, transparent to VUV light,
and a CsI photocathode deposited on the first THGEM. A gain of $8\cdot10^{5}$
per photoelectron and $\sim100\%$ photoelectron collection efficiency are
measured at stable operation settings. The excellent position resolution
capabilities of the detector (better than 100 $\mu$m) at 100 kHz readout rate,
is demonstrated at room temperature. Structural integrity tests of the detector
and seals are successfully performed at cryogenic temperatures by immersing the
detector in liquid Nitrogen, laying a good foundation for future operation
tests in noble liquids.
