Specifically, the idea of a shell protecting an isolated space.
Street
Suzhou Museum / I.M. Pei
A path connecting two spaces that might be difficult to reach without one.
Exhibition
Guggenheim Museum / Frank Lloyd Wright
Forcing one to take a closed path.
Sacred
Notre Dame de Haut / Le Corbusier
Thick wall with opening that are small, but also large at the same time.
Congregation
Shogin Tact Tsuruoka / SANAA
I find the many flowing roofs leading to a cube block very inviting and intriguing. Also, the idea of having no main entrance but rather entrances from all direction is key for a space of congregation.
Learning
The Einstein Tower / Erich Mendelsohn
This curved room with many rounded windows creates an optimal learning environment.
Commerce
Rogier Square, Brussels / Xaveer de Geyter Architects
Attraction that draws interest, open for gathering and activity.
Living
Maison Bordeaux / OMA
The concept of having contrasting spaces to live in. Open/closed, straight/curved, dense/light.