The antonyms for the word "field days" could be "indoors," "city life," "urban environment," "confinement," and "restriction." These terms represent the opposite of the open, outdoor, and free-spirited experience that "field days" connotes. Instead of engaging in games, sports, and team-building activities in a natural setting, antonyms of "field days" imply a more closed and limited environment where people are confined to tight spaces and restricted by rules or protocols. However, it is worth noting that these antonyms are subject to interpretation and can vary based on personal preferences and experiences.