Hong Kong is small, and a day trip here usually means a ferry or forty minutes on the MTR rather than a long drive.
Macau — 1 hour
The former Portuguese colony, across the Pearl River estuary. A UNESCO-listed old town of baroque churches and calçada paving, the largest gambling economy in the world, and egg tarts.
Ferry from Sheung Wan or Kowloon, or bus over the Hong Kong–Zhuhai–Macau Bridge.
Take your passport — it is a full immigration crossing.
The outlying islands — 30 to 60 minutes
Cheung Chau for the fishing harbour and the Bun Festival; Lamma for the cross-island walk and seafood; Peng Chau for quiet.
All car-free, all from Central Piers, all on Octopus.
Lantau — 40 minutes
The Big Buddha and Tai O make one good day. Mui Wo has a beach and the start of the Lantau Trail; Pui O has water buffalo on the beach, which is not a metaphor.
The New Territories — 1 hour
The half of Hong Kong that most visitors never see.
Ping Shan Heritage Trail for the Tang clan’s walled villages and a 1380 pagoda. Wetland Park for the birds on Deep Bay.
Sai Kung in the east for seafood on the waterfront and boats out to the beaches at Tai Long Wan.
Sha Tin for the Ten Thousand Buddhas Monastery — 400 steps lined with gilded arhat statues — and the Hong Kong Heritage Museum.
Tai Po and Fanling for market towns and walled villages.
Shenzhen — 45 minutes
Across the border, and a genuinely different proposition: a city of 17 million that was a county town of 30,000 in 1979, and is now China’s technology centre.
East Rail Line to Lo Wu or Lok Ma Chau, or the high-speed rail from West Kowloon to Futian in 14 minutes.
You need a visa. Most nationalities require a Chinese visa arranged in advance; a five-day Shenzhen special economic zone visa has historically been available at some border crossings for certain passports, but eligibility and availability have changed repeatedly. Check the current position with the Chinese embassy rather than relying on any guide.
Also worth knowing: mainland China has a different internet, and Google, WhatsApp, Instagram and a great many other services do not work without a VPN arranged beforehand. Alipay or WeChat Pay are effectively required for payment; cash is increasingly refused.
Guangzhou — 1 hour
High-speed rail from West Kowloon. Same visa and payment considerations.
Practicalities
Ferries and MTR are on Octopus; cross-border services are not.
For Macau and the mainland, allow time for immigration queues, which at Lo Wu on a weekend can be substantial.
Typhoon signals suspend ferry services entirely — check the Observatory before setting out for any island.
Choosing between them
One spare day and you want something completely different: Macau. One spare day and you want the landscape: Lantau or Sai Kung. Interested in what was here before 1841: the New Territories and Ping Shan. Travelling with children: Cheung Chau and a bicycle.
Timing and tickets
Ferries to Macau run through the day and book out at weekends and around holidays — reserve online in advance if you have a fixed plan.
Outlying island ferries need no booking but do have gaps in the timetable; check the last sailing before settling in for dinner.
Cross-border rail to Shenzhen and Guangzhou from West Kowloon requires tickets and a passport, and immigration is done in the station.
The weather caveat
Typhoon signal 8 suspends all ferries and most buses, and signal 3 can suspend outlying island services in rough water.
Every one of these day trips depends on a boat or a long road journey. Check the Observatory the night before between June and October.
What each one costs in time
Macau: an hour each way plus two immigration queues, so budget ninety minutes door to door in each direction. A full day.
Cheung Chau or Lamma: thirty to sixty minutes each way. A comfortable half day, better as a full one with a meal at the end.
Lantau: forty minutes to Tung Chung, then the Buddha and Tai O. A full day.
New Territories: an hour to Ping Shan or the Wetland Park. Half a day each, and they combine.
Shenzhen: fifteen minutes by high-speed rail from West Kowloon, and considerably longer through immigration. Only worth it if you have the visa and the payment apps sorted in advance.
Doing it independently
Every destination on this list is straightforward on scheduled transport, and organised tours to Macau, Lantau and the islands cost several times the fare for the same places on a fixed schedule.
The exception is anywhere in the closed border area — Mai Po nature reserve in particular requires a permit and is normally visited on a WWF-led tour booked well in advance.