1. v.;the exploration of natural caves
2. v.;the exploration of a man's anus by either: A. himself, B. a female sex partner., or C. male sex partner.
2. while watching porn: "Eww, did you see her slip her finger into his butt? She's totally into spelunking."
To engage in casual internet stalking, usually out of curiousity rather than for any sinister purpose.