From safe on Isle of The Sea Hag go n;w;w;w;w;n and look in the stump, and check the stump in the north room too. Should either contain a "a carved wooden statue" take it out. Then go back to the first stump if you are not already there, and kill the mechanical man, you need to kill him until you have both a blue and a green eye.
Once you have both, head back to safe, place the two eyes into the idol in the room, and then place the statue inside. Take out the key that will now be in there, and head n;n;w;n;n;n;n pick lock the north door, north, bash west, west, disarm west, west, search, take the key, e;e;s;e;e unlock northwest, nw;d;se;s;s;se;s;d;e;s;u;s (south again is a death trap) and finally east. Unlock the coffin and get all from it.
Note: The statue is vanish death, so hide it somewhere safe if you are not to certain.
A Seashell-Decorated Coffin contains:
Item 'a moonstone cabochon' is type artifact, alignment 0, made of stone, has keywords 'moonstone cabochon white stone'. This item weighs 0 stones and 10 pebbles, and is valued at 16,500 gp. This level 200 item has the attributes: identified unique A moonstone cabochon is in excellent condition. Has 10 of 10 total charges per day of level 200 spell 'cure serious'. *Your class must be something other than priest to use this item. *Your level must be greater than or equal to 200 to use this item. *Your sanity must be greater than or equal to 20 to use this item. *This item has a limit of [3] per character. This shimmering white moonstone has been cut into a large cabochon and is glowing faintly, lit up by some inner power. The stone feels rather warm to the touch, and gives you a faint, reassuring tingle all over your body. Item 'a tanzanite cabochon' is type artifact, alignment 0, made of stone, has keywords 'tanzanite cabochon purple stone'. This item weighs 0 stones and 10 pebbles, and is valued at 28,500 gp. This level 240 item has the attributes: identified unique A tanzanite cabochon is in excellent condition. Has 7 of 7 total charges per day of level 241 spell 'rejuvenation'. *Your sanity must be greater than or equal to 20 to use this item. *Your level must be greater than or equal to 240 to use this item. *This item has a limit of [3] per character. This deep purple tanzanite stone has been cut into a large cabochon and is glowing faintly, lit up by some inner power. The stone feels rather warm to the touch, and gives you a faint tingling sensation in your pineal gland.