When you begin Harvest Moon DS you can quickly make some money by visiting the excavation site in the northeast corner of the valley. The excavation site is currently being treated by Carter and Flora as an archeological area. At the beginning of the game you can visit their site and use your hoe to dig up such items as Sunblock, Earrings, Necklaces, and so on.
(Perfume appears in year 6)
The easy way to dig up the items from the excavation site is to save your game at the entrance, then dig around with your Hoe until you find one. When you reload your game the item will still be in the same spot, which saves you wear on your stamina levels.
The excavation site also contains 4 hidden mines. To unlock the first mine you need to visit the site in the hours when nobody is in the excavation site, either very early in the morning or after 9:00 pm. Carter will be in the site by himself, and he is in need of your hammering expertise. When you hit the wall as Carter instructs you will open up a doorway to the first mine. All of the mines will need to be unlocked by Carter and your Hammer.
1st Mine: 10 Floors
To progress down into the mine you may fall down holes hidden in the ground. You can dig for the staircase like you may have done in Friends of Mineral Town, but it's much more efficient to fall down the holes. At the bottom of this mine you'll find a wild, aggressive bird. You have to hit the bird with your tools in order to destroy it.
The tool you use will determine how much damage you do to the Dark Creature. A Hammer or Hoe does a small amount of damage, the Sickle and Axe do a medium amount, and the Legendary Sword (see mine 2) does the most. You can't fight with your Watering Can.
2nd Mine: 255 Floors
When you have cleared the 1st mine you can activate the 2nd mine. Visit the excavation site as you did before and assist Carter with smashing the wall. The second mine is 255 floors deep, and you can only fall (at most) 10 floors at once. This mine has a lot of wild animals to fight off, but when you reach the bottom and clear away the enemies you will discover the Legendary Sword. You can pick it up if you have at least 1 of your tools at Mystril upgrade level (400%) in HMDS, but in HMDS CUTE you must have all of your tools at Mystril (Axe, Fishing Pole, Hammer, Hoe, Sickle, and Watering Can).
(In the English HMDS Keria gives you the sword. In the Japanese version it is just laying on the ground for you to collect.)
You must destroy the creatures on the 255th floor for the rock blocking the room with the sword to dissolve. You can't cheat by saving your game and then turning off your DS, expecting the creatures to all be gone when you reload. The creatures will be gone but the rock will also still be there.
You can use this sword to clear away the large rocks that protect the Super crop field behind the waterfall. To use the sword to destroy the rocks, place it in the red slot in your rucksack then press the A button. You will swing the sword and the giant rocks will go away.
The sword's main use is just for destroying the large rocks. You can also use it to fight off the creatures in the mines if you equip it and press the Y button. If not, you can just store it inside your house once you're finished with it.
3rd Mine: 999 Floors
To unlock the 3rd mine, reach the bottom of the 2nd mine and clear away the animals. Then activate Carter's hammer event again. This 3rd mine has 999 floors and it does contained the cursed tools and accessories. You can find the tools hidden in the ground on specific floors. You can find the secret sleeping princess, Keria, on the 255th floor of the mine.
4th Mine: 65,535 Floors
The last mine unlocked is a whopping 65,535 floors deep. You can fall up to 300 floors at a time! The special items in this Mine are colored balls called Wonderful Stones, which you'll find on floors ending in 0. If you collect all 9 colors, the Goddess will appear and grant your choice of 3 preselected wishes.
To unlock the mine make sure you've triggered Keria's Black Heart Event n the 255th floor of the 3rd mine. You also need to have cleared the bottom floor of the 3rd, just like with the previous two mines. Then just activate the mine discovery event with Carter one last time.
You don't have to complete the Black Heart Event, and it does not trigger if you are already married.
At floor that end in 00 (200, 1000, etc.) you will be greeted by Mayor Thomas, who is hidden behind a large stone. If you destroy the creatures on the floor you can talk to him. Thomas will offer you items to eat in order to recharge your stamina, but he charges extraordinary prices for them.
You can save while you're going through the mine, and you don't have to use both save slots like the GBA versions. Dead End floors are very rare but saving your game allows you to control how far you fall. If you go too far down a hole then just reload and try again. Saving occasionally will also allow you to reload if you run into some... unexpected... situations. When you are hit by a dark or evil creature you are pushed backwards. There's always the chance you might be pushed beyond the wall!