Here are the primary antonyms, categorized by context:
An alcove is defined by being a that opens onto a larger room or area. Therefore, its most accurate antonyms describe the opposite: projections, open expanses, or unbroken surfaces.
While “alcove” doesn’t have a direct, perfect antonym, the best opposite depends on which aspect of its meaning you want to contrast.
Here’s a text explaining the antonyms clearly: