Often when we think of sanctuary, we think of refuge, a safe place. A sanctuary is also a holy or sacred place. It doesn't have to be a building, it can be within us.
I had to build a sanctuary within myself when I was a kid. It started out as a safe place, a place that could insulate me against a very loud, chaotic, overwhelming world. I built it stone by stone, a place of quiet, a place to recharge. As I got older and my coping mechanisms became more ingrained, my sanctuary slowly shifted to a place to contemplate, it became the silence I needed to contemplate and worship the divine. It also became the place where my memories were stored, where all my life experiences were kept as works of art, as an old library.
It took several mental exercises, imagination and necessity to create this place. Before I would go to bed I would build my sanctuary a little bit more, add a little more detail, add another memory to my collection.
I later found out that this process had been done before. If you are curious about memory and internal sanctuaries (or palaces). The Memory Palace of Matteo Ricci by Spence is a good place to start.