mausoleum vs undercroft

mausoleum

noun
  • A gloomy, usually large room or building. 

  • A large stately tomb or a building housing such a tomb or several tombs. 

undercroft

noun
  • A cellar or vaulted storage room. 

  • A ground-level car park that occupies the base of a building. 

How often have the words mausoleum and undercroft occurred in a corpus of books? (source: Google Ngram Viewer )