A separate border, like Hong Kong
Macau runs its own immigration: passport holders of about 90 countries and territories enter visa-free for stays of 30–90 days (British passports: 180 days). Visa-free entry here does not admit you to mainland China, and a mainland visa does not admit you here.
The old town is UNESCO and free
The Historic Centre of Macao, inscribed in 2005, is roughly two dozen monuments and squares within a 20-minute walk — Senado Square, the Ruins of St. Paul's, A-Ma Temple, the Guia Fortress. None of them charges admission.
The free casino shuttles are a real transport network
Every big resort runs free coaches between the airport, both ferry terminals, the border gate and its own door, roughly every 15 minutes. Locals ride them too — treat them as an unofficial city bus service.
Hong Kong dollars work at 1:1
The pataca (MOP) is the official currency, but HKD is accepted at par almost everywhere, and Alipay or WeChat Pay QR codes cover most shops and all buses. Keep small bills for taxis and the tiny egg-tart bakeries that are cash-only.