Talking about the sacrum and how it supports the entire spine. In another modality, I learned and experienced that the ilia and the temporal bones in the head mimic each other. When someone was working on my temporal bones with little pressure, I could feel them moving in sync with my ilia. This was a VERY subtle sensation!
Many massage therapists I know shy away from working on the posterior hip/sacrum area. I find clients, especially those with low back or leg pain, receptive to massage in this area once the relationship is explained to them.