Updated on 15/7/2020: The bug has been fixed in the patch by Nintendo so it is no longer accessible through this method.
It is entirely possible to access Lake Mine during non-Winter season with the help of existing bug in game. For unaware players, this bug has existed since older version (we are talking about Nintendo Game Boy here). It is certainly a nice surprise to see it ported to the Nintendo Switch remake, considering one would have thought they will fix it. Anyway, we will be covering one of the ported bugs here.
**For players who wish to play Story of Seasons: Friends of Mineral Town fairly, you should turn back now, because this is not the article you should be reading.**
For starters, you can perform this trick anytime in any day. It is not advisable to perform it during late evening or midnight in game, since time do pass in mine. You can read about it here if you need more details on this. Similarly, bring your tools (hoe and hammer) along, and perhaps some food too to restore your stamina.
Now, for the main deal. You will want to head first into the Spring Mine, and come out. Do not move and save your game at the entrance. From here, you need to load your game, and push your left analog stick up while it loads. You will find yourself running up to the river above.
When you are at the river, look for the shore that has slightly darker texture on them (see image below). Head there and push your left analog up again to push forward the wall all the way. You will find yourself dropping down into a plain field.
Go left in this field, until you see a light source shaped similar like the image below. Head south from this position.
If you have done this correctly, you should find yourself glitched to a graphic that looked like the pathway to the top of the mountain. If yes, head left. Else, you may want to retry from the very beginning.
When you are heading left, you will see your character dropping into a plain field once again. Here is the slightly trickier part. You will want to make your character go left (or right) until you are able to find the invisible space to go south. If you are successful, you will find yourself under the shadow of some trees. Do not walk out from the shadow or you may have to retry the whole sequence again.
Venture into the plain field again, and attempt to work your way out by using the tree shadows as your guide. The correct direction should be more south, then head right. A good sign is when you see a row of trees like the image at the bottom. This is where you want to head right along the tree shadow. Again, do not walk away from the shadow.
If all done correctly, you should be able to exit from the shadows and step on top of the lake. Being able to perform this is equivalent to a successful attempt. Well done, comrade! Go ahead and mine until your heart desire.
Getting Out from the Mine
So, you have mine what you need and wanted to go back now? You should find yourself unable to walk away through the lake like how you came in. Fret not, because here are how you can return back to your home sweet home.
Method 1 – Wait until 6:00 AM (Not Recommended)
This should be straightforward. All you have to do is to stay outside of the mine and let time ticks until 6:00 AM. You will automatically faint and be transported back to your house. No day will be lost, but you will start your day in a reduced stamina, which is also why such method is not suggested.
Method 2 – Deplete Your Stamina (Recommended)
The better way of getting out is to deplete your stamina until you faint outside of the mine. Keep using your tools until your character faints and be transported into the Clinic. Again, no day will be lost and you start your day in full stamina. No penalty or whatsoever.
Lastly, considering you will be starting a new day after mining, it is highly suggested for player to finish feeding their animal or watering their crop before heading to the mine. Otherwise, have fun smashing the stones away.