Glasgow's two football clubs — Celtic and Rangers — define much of the city's social and cultural life in ways that require explanation to outsiders. The Old Firm rivalry between them is one of the most intense in world football, historically loaded with sectarian division (Celtic traditionally Catholic and Irish-descended, Rangers Protestant and unionist) though this dimension has diminished significantly in recent decades.
Celtic Park (in the East End, capacity 60,000) and Ibrox Stadium (in the South Side, capacity 50,000) both offer stadium tours and have museums attached covering each club's history. Attending an actual match between the two clubs — an Old Firm derby — is a formidable cultural experience, though tickets are almost impossible to obtain without connections. League matches against other clubs are more accessible and still give a genuine sense of how seriously Glasgow takes football.