Identifying this corbelled arch

Hi, we saw this stone arch just east(?) of the royal palace grounds. It’s unusual in that it’s a corbelled arch, something that was used many hundreds or even thousands of years ago. Does anyone know why it’s here? What is the building that it’s attached to?

Here’s the image on Google Street View:
https://www.google.com/maps/@59.918473,10.7316997,3a,75y,314.18h,88.06t/data=!3m6!1e1!3m4!1sBBFm_PZop5J6F8poPUQ_Xg!2e0!7i16384!8i8192