There are two separate areas of B2. The first you will encounter climbs toward the crystal room, and includes four Treasures and an HP/MP Spring that you should take advantage of. Don't waste the Antarctic Winds you find here, as they can make short work of the Altar Cave's boss. The Monsters here are nothing special, though they do sometimes appear in large groups.
If you return to the cave later, from the main entrance, you'll find the pit leading to B3 in a room with some more Treasures. You'll find two Longswords that Warriors can make use of, as well as Nunchaku for a Monk and the Sleep Spell for a Black or Red Mage.
If you return to the cave later, from the main entrance, you'll find the pit leading to B3 in a room with some more Treasures. You'll find two Longswords that Warriors can make use of, as well as Nunchaku for a Monk and the Sleep Spell for a Black or Red Mage.