Any ancient ruins in Egypt will be on land.
That is not entirely true. You can dive ancient ruins out of Alexandria. The city is on the Mediterranean coast rather than the Red Sea and is admittedly not mainstream Egyptian diving, but the opportunity exists for someone with a strong interest.
The most popular dive site in the area in Cleopatra’s Underwater City which is full of sphinx statues and Roman columns. This city, which was built by Alexander the Great in 300BC, collapsed into the sea after an ancient earthquake. Other ancient sites include Lighthouse and Fort Qaitbey.

Diving in Alexandria | PADI
Learn key information about diving in Alexandria, Egypt - when to go, what to see, who to dive with, top marine life, recommended training & more.