A reference to Downton Abbey, a British television drama about an aristocratic family and their household staff in the early 20th century.
A made-up place name (down + ton, suggesting a village or country estate) created for the TV series, though 'down' is common in English place names (South Downs) and 'ton' means settlement.
Downton Abbey became so culturally dominant that people use 'Downton' to mean fancy British period drama—the show basically trademarked an aesthetic and a level of sophistication in television!
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