Mount Pinatubo, about 25 kilometres west of Angeles City, is the region's most dramatic day trip. The 1991 eruption that devastated the surrounding area also created one of the most spectacular landscapes in the Philippines: the caldera left behind by the collapse of the summit now holds a stunning blue-green crater lake at roughly 800 metres elevation. Trekking to it — through grey lahar canyons, past still-steaming vents, and up into cloud-wreathed highlands — is an all-day undertaking that rewards the effort.
You will need a guide and usually an off-road vehicle for the approach, which starts from the village of Santa Juliana in Capas, Tarlac. The dry season (November to May) offers the most reliable conditions, though even then you should start early — afternoon clouds regularly obscure the crater. Some operators offer helicopter overflights from Clark Field for those who want the view without the hike.