What it is
Dahab is a small, low-rise town on the Sinai coast, built around shore diving, with reefs a few metres from the beach and a long-standing backpacking scene. Marsa Alam, on the mainland coast further south, is a string of resorts with house reefs, dugongs in the seagrass bays and boat access to offshore sites. Hurghada and Sharm el-Sheikh are the large package-resort versions of the same coast.
Why go
The reefs are in good condition by global standards and the visibility is reliable. Dahab suits independent travellers and people learning to dive; Marsa Alam suits families and anyone who wants to step off a plane and into a resort. Snorkellers get plenty here without a certification.
When to go
All year. Water is warmest in August and September at around 28-29°C and coolest in February and March at around 22°C, when a 5mm wetsuit is worth having. Summer air temperatures pass 40°C on the mainland coast, though the sea and the breeze make it manageable. Do not fly within 18 to 24 hours of your last dive. Dahab's Blue Hole is a well-known site with a bad safety record: the shallow rim is fine for snorkelling, the deep arch has killed a large number of divers, and no recreational diver should be attempting it. Check your government's current travel advice for Sinai before booking that side.
Most people stay 4-7 nights.