Several has to be the subject since 'of the caves' is a prepositional phrase and 'are open' is the verb.
Ronal C. Kerbo has written: 'Caves' -- subject(s): Caves, Juvenile literature, Speleology 'Caves' -- subject(s): Caves, Juvenile literature, Speleology
Tony Waltham has written: 'Caves' -- subject(s): Caves 'Sinkholes and subsidence' -- subject(s): Sinkholes, Subsidences (Earth movements), Engineering geology, Earth movements and building 'Yorkshire Dales' -- subject(s): Pictorial works, Geology, Landscape, Guidebooks, Landscapes 'The limestones and caves of northwest England' -- subject(s): Caves, Karst 'The world of caves' -- subject(s): Caves
caves
Not quite sure what you had in mind but someone who searches for, and explores,caves is a Caver - as simple as that. The technical term for one who studies caves and their contents scientifically is "Speleologist".
David C. Culver has written: 'Encyclopedia of caves' -- subject(s): Caves, Encyclopedias, Speleology 'The biology of caves and other subterranean habitats' -- subject(s): Biospeleology, Cave ecology
Troglodytes live(d) in caves.
Compassion of Buddha
Spelunkers like to explore caves.
The found the geode while travelling through the caves. This is a sentence containing the word geode.
Peter M. Hauer has written: 'Caves of Massachusetts' -- subject(s): Caves, Guidebooks
Well, depending on what type of cave we are talking about here (Underwater caves, Underground caves, Mountain range caves, Man-made caves) you can likely derive your own conclusion with some simple research. Caves, in general, do not really belong to any specific Biome. All biomes have some kind of cave somewhere on earth. There are caves on every corner of the earth so the answer to your question is that there are caves in every Biome.
Edmund J. Mason has written: 'Caves and caving in Britain' -- subject(s): Caves, Caving