Eastern Visayas is an administrative region also known as Region VIII. It consists of three main islands, Samar, Leyte and Biliran, which are close together and connected by bridges. The geology is rather complicated and there are numerous resources, including chromite, uranium, gold, silver, manganese, magnesium, bronze, nickel, clay, coal, limestone, and pyrite.
As you can see the list includes limestone, there are numerous areas which are covered by limestone and are karstified. There are two "borderline" show caves, and an abundance of small undeveloped caves which are guided as cave trekking tours by someone. Caving in the tropics is either quite comfortable, due to the high temperatures and the locals do it in T-shirt, shorts and flip-flops. Or it is quite nasty with snakes and other crawly creepies, histoplasmosis and other diseases. Depends obviously on your point of view.