It is well-known that most of the surface of our planet is covered by water. Land is intrinsically valuable and, with the exception of a few ambitious projects of land reclamation, they don't make it any more.
However, just like anything else, land can be over-priced. The realistic value of land depends not only on supply and demand, but also on its context and material. Land that is valued by the seller on the basis of an assumption (perhaps the development of an urban infrastructure), is almost certainly over-valued unless the buyer has control over the reality of that assumption, or may defer part of the payment until that assumption is fulfilled.