A spade is required to get into Olaf's Cave, as well as completing part of Olaf's Quest
. Brine rats require a slayer level of 47 to kill as a task and they give 50 slayer XP. They seem to be weak to Magic attacks and stab attacks. They also are quite popular for the amount of gold charms they drop.
Charm Drop Rates
Eww, a bald rat!
Brine sabre, Starved ancient effigy
Bones (100%), Raw rat meat (100%), Coins (1-34), Blood rune (4), Water rune (10-18), Earth rune (10-36), Air rune (18), Death rune (7), Water talisman, noted Raw rat meat (18), noted Raw pike (18), Raw swordfish (9), Raw shark (2-7), noted Raw lobster (10), noted Raw shark (2-8), Shark(1), Gold charm, Green charm, Blue charm, Crimson charm