Shenzhen
Shenzhen works best as a district plan rather than a single downtown: Futian for the high-speed rail hinge with Hong Kong and for MoCAUP at the civic centre; Guangming for the science museum and SIMoA; Pingshan for the Natural History Museum at Yanzi Lake; Longhua for the Art Museum new hall near Shenzhen North. Metro Lines 3, 4, 6, and 16 cover most museum days if you keep one district per half-day. Cross from Hong Kong via West Kowloon to Futian high-speed rail or East Rail to Lok Ma Chau / Lo Wu, and book museum tickets on WeChat before you clear immigration.