When cast, how do physical barriers affect the range of Gravity Sinkhole? Can the spell's effect be felt through walls, dirt, rock, and water, for example, or is it effectively limited by the volume of available open space?

AoEs are blocked by anything that would constitute total cover (like walls). Some AoEs can go around corners - if they do, they specifically say so.

Chapter 10: Spellcasting >> Casting a Spell >> Areas of Effect

Areas of Effect

Spells such as Burning Hands and Cone of Cold cover an area, allowing them to affect multiple creatures at once.

A spell's description specifies its area of effect, which typically has one of five different shapes: cone, cube, cylinder, line, or sphere. Every area of effect has a point of origin, a location from which the spell's energy erupts. The rules for each shape specify how you position its point of origin. Typically, a point of origin is a point in space, but some spells have an area whose origin is a creature or an object.

A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover.

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Sphere

You select a sphere's point of origin, and the sphere extends outward from that point. The sphere's size is expressed as a radius in feet that extends from the point.

A sphere's point of origin is included in the sphere's area of effect.

Got it! Thanks.