A little tricky! 😄
As Visuhole makes a perfect Drill, Carve, Emboss..
Scale your object, scale your Stencil
Apply Visuhole for the groove
And Slice! (With Su_Slice by Suforyou)

GIF_visu_slice.gif

Maybe some Guide lines will be necessary...

GIF_visu_slice02.gif

Will be the same for your mountain surface! 😄

bloc.jpg