A theme from the Pokémon Mystery Dungeon Series. Despite the title, this song doesn't really sound like a cave theme at all (at least for SMW levels). This theme is a nice tune that is more fitting for mountainous environments, grasslands, and sometimes deserts.
UPDATES: Replaced the nylon guitar for a steel guitar. Added more instrumentation to the beginning. Increased the echo reverb and delay. Various volume and panning changes.