Spring 5

The door is shut until Spring 5 of year 1. Morris's letter that morning is the signal. Walk to the mountains, north of the carpenter's shop.
Marlon hands you a Rusty Sword on the first step inside. The elevator is already there. It only lists multiples of 5 you have reached, so the first trip is a walk from floor 1.
Copper ore starts on floor 2. Break copper nodes for 1–3 ore. Ordinary rocks on those floors can drop a single piece too. One ore is enough for Clint to visit the next morning with the furnace blueprint: 20 copper ore and 25 stone.
A short loop
Smelt a copper bar with 5 ore and 1 coal. The furnace takes 30 in-game minutes. Sell price of the ore is 5g, so the bar is the point of the trip, not the ore pile.
Stop at the next multiple of 5 when you are low on health or the day is late. Floor 5 is the first elevator stop. Floor 12 has six coal and a ladder that is already on the floor. Leave before 2:00 am. Empty energy or 2:00 am costs 10% of your gold, up to 1,000g, and you wake at the entrance.
Empty health is harsher: 5% to 25% of your gold, up to 15,000g, plus lost items. Tools come back in the mail the next day. Fishing poles and weapons do not. The Galaxy Sword is kept if you already have it. Marlon sells one lost stack back at its base sell price.
Upgrade the pickaxe at Clint when you can pay and spare the days without it. A steel pickaxe, or a bomb, opens the dwarf's door on the entrance floor. Cherry bombs unlock at mining level 1 and cost 4 copper ore and 1 coal.
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