Nellitheertha Cave is a low-roofed cave temple north of Mangalore, with a small lake and a Shiva lingam inside. The appeal is the mix of pilgrimage site and natural cave: visitors enter a narrow, damp space rather than a conventional temple hall.
Bring footwear and clothes you do not mind getting muddy, and check local opening conditions before going. It is best treated as a half-day side trip from Mangalore rather than a quick city stop.