long, open, level area, usually next to a river or a (former) miltary building where people may walk

An esplanade is a long, open, level area. It is usually next to a river or large body of water for people to walk on. This allows people to promenade along the sea, usually for recreational purposes. They can ignore the state of the tide and do not have to walk on the beach. Esplanades became popular in Victorian times when it was fashionable to visit seaside resorts.

Esplanade in England