Do turtles / tortoises / snails feel trapped in their shells?

No more than you feel trapped in your skin. The shells of the creatures you named are part of their skin, not external things they have to carry around. The closest human analogy would be our fingernails/toenails. read more

Due to their slow speed, tortoises ( and turtles and terrapins) have had to develop especially hard shells in order to protect themselves from predators. These shells are strong enough that they have been known to withstand bullets, dogs and even alligators. read more

Turtles also do not have nerve endings in their shells but touching it causes a shift in the tissues that keep it attached to their bodies. This can be compared to the way you cannot feel your hairs or fingernails being touched but rather them being pushed or pulled from the tissues that they are rooted in. read more