I have built and consulted on a number of caves and underground aging areas. For it to be done right requires significant time and effort. I would say 50% of the caves I have seen as miserable failures beyond redemption. They have wild temperature fluculations and incorrect airflow/ventilation. Another 45% have rectifiable major flaws. The last 5% were built on multi-million dollar budgets, incorporate sophisticated temperature control systems and work beautifully.
It is possible to build a cave in a hill side and have it work beautifully but, unfortunately, most small producers who are doing this lack the expertise or funds to hire epxertise to make it work.