The art makes the walls look like they have low-quality textures, I was convinced it was 3D renderings at first.
You would probably have a similar experience in the Lærdal tunnel. https://en.wikipedia.org/wiki/L%C3%A6rdal_Tunnel
To counter this, the tunnel is broken up somewhat by three caves blasted out at regular intervals; these are lit by coloured lights and go a ways towards breaking the monotony.
Still mind-numbingly boring, though.
To give an idea of how prevalent tunnels are in western Norway - going from where I live in Hareid down to where my mother's family comes from, Voss - a 400km/250mi drive - just over 100km/62mi are in tunnels, including the Lærdal tunnel and the Eiksund tunnel, which was until recently the deepest subsea road tunnel in the world at 290m/950ft deep. (Steepest grade: 9.6%. Engine braking is your friend.)
Don't remember exactly, but I think the first part is uphill, then flat, then downhill. You can see it very clearly on the performance monitor. There's also the built-in curves, of course, but I guess that's pretty standard road tunnel engineering.
Cement rendering is the application of a pre-mixed layer of concrete, possibly colored, onto a surface. Per the wikipedia link.
Render images can be found here: https://www.estunlar.fo/fo/um-tunlarnar/eysturoyartunnilin/