The Etherealness spell states:
You ignore all objects and effects that aren't on the Ethereal Plane, allowing you to move through objects you perceive on the plane you originated from.
When the spell ends, you immediately return to the plane you originated from in the spot you currently occupy. If you occupy the same spot as a solid object or creature when this happens, you are immediately shunted to the nearest unoccupied space that you can occupy and take force damage equal to twice the number of feet you are moved.
For the purpose of these rules, an object is a discrete, inanimate item like a window, door, sword, book, table, chair, or stone, not a building or a vehicle that is composed of many other objects.
I assumed that Etherealness allowed travel through walls, as they are composed of multiple objects; however, this answer implies a composition of objects is not an object. Additionally, if a wall or large object like a vehicle is not an object, what is the point of the damage/ejection clause in the spell? I'd like to know what the limits are for passing through things on the Ethereal Plane. In particular, please answer the following questions with as much RAW support as possible:
- Is it possible to pass through a building?
- Is it possible to pass through the ground?
- Is there anything that has mass and is neither a creature nor an object? If so, please provide examples and indicate whether it falls into an explicit class of its own, analogous to objects and creatures.
If the answer to either of the above is no, I am interested in a lore-based reason why this isn't possible.