<human>:  What are the best cities to live in for a single person in their 30s?
<bot>: The best cities to live in for a single person in their 30s depend on many factors, such as career opportunities, amenities, cost of living, and cultural attractions. Some of the most popular cities for singles in their 30s include New York City, San Francisco, Chicago, Seattle, Houston, Los Angeles, Denver, Amsterdam, Barcelona, London, and Berlin.