What's the must-see thing in Cancun?

MUSA sits in 3 to 6 metres of warm Caribbean water between Punta Cancún and Punta Nizuc, inside the national park established in 1996. The visibility on a calm morning tends to run 15 to 20 metres and the water temperature holds around 28°C through June and July. You'll float above Jason deCaires Taylor's concrete figures while sergeant major fish pick at the coral that has grown over their shoulders. The salt taste of the Caribbean clings to your lips for hours. Snorkel tours leave from marinas along Boulevard Kukulcán in the Hotel Zone and cost about 50 USD per person, roughly 870 MXN at current rates. Glass-bottom boat alternatives run closer to 30 USD. Worth noting, the Punta Nizuc section is shallower and calmer, better for nervous swimmers. Book a morning departure, because afternoon swells off Isla Mujeres chop the surface and can cut visibility below 10 metres.

El Rey stands at Kilometre 18 on Boulevard Kukulcán, the single road that runs the length of the Hotel Zone's narrow sandbar. The site covers a Late Postclassic Maya settlement, likely 1200 to 1500 AD, and the remains are low stone platforms and a small pyramid about 5 metres tall. Honestly, the ruins are modest compared to Tulum or Cobá. The draw at El Rey is its resident colony of iguanas. Hundreds of them bask on the warm limestone, completely unbothered, some longer than your forearm. Admission is around 95 MXN and 30 minutes is plenty. Go around 16:00 when the low sun throws long shadows across the stones and the iguanas are still soaking up 30°C heat. You can walk here from most Hotel Zone properties.

Museo Maya de Cancún opened in 2012 on the grounds of the San Miguelito archaeological site at Kilometre 16.5 of Boulevard Kukulcán. It holds over 400 Maya artefacts from across the Yucatán Peninsula, including pieces from Palenque and Chichén Itzá that rarely travel. The building is air-conditioned to about 22°C, which feels like a different country when you step in from the 34°C sidewalk. Admission runs 95 MXN and includes access to the San Miguelito ruins behind the museum, a forested trail where you'll hear parrots overhead and the ground smells of damp earth and leaf rot. That said, the Museo Maya's English signage is thin in places. A 15-minute read of the Cancún section on Wikivoyage before you go fills the gaps the placards leave. Skip the Chichén Itzá day trip on your first visit. The drive is 3 hours each way through flat scrubland, and you'll spend more time on the bus than at the site.