Once you have completed the 'Tribute to Murals' Adventure - https://adventurelab.page.link/HsTq - you will have gathered the information required to find this bonus cache.
X = M + R
Y = L - M
Z = A - U
The cache can be found at S 41 1X.YZY E 173 1.Z.YZZ
The cache is a micro container with log only so please bring your own writing device.
Enjoy.