Refer to this for room locations.

Take the fuel canister and the lamp in the Lighthouse storage room. Use the canister on the fuel barrel to fill it with fuel.
Go to the 2nd floor. Hold the use key on the crank and spin it till completion.
Go into the light room. Use the canister on the light's fuel hole.

Refer to this for locations of points of interest.

OPTIONAL Pick up the suitcase on the Dock. Go to your House. Put the suitcase on the table in the bedroom. Take the "lighthouse" medallion from the suitcase and place it into the chest.
Pick up the key from the bedside table in your House.
Go into the Lighthouse light room. Pick up the canister.
Go into the storage room. Pick up the lamp. Fill the canister with fuel.
Go to the 2nd floor. Use the crank.
Go into the light room. Pour the fuel into the light.

Pick up the key, the lamp and canister from the table of your bedroom.
OPTIONAL Go to the boat and pick up the "eye" medallion. Place it into the chest in your bedroom.
Go into the Lighthouse storage room. Fill the canister with fuel.
Go to the 2nd floor. Pick up the cloth.
Go onto the balcony. Use the cloth on all 8 windows.
Go into the Shed. Pick up the rope.
Go outside. Pick up a bag of grain.
Go to the Lighthouse 1st floor. Put the bag of grain on the floor.
Go to the Shed area. Pick up a bag of grain.
Go to the Lighthouse 1st floor. Put the bag of grain on the floor.
Run into the shed. Go outside. Pick up a bag of grain.
Go to the Lighthouse 1st floor. Put the bag of grain on the floor.
Go to the 2nd floor. Attach the rope under the crank.
Go to the 1st floor. Pick up the bags of grain and attach them to the rope one by one.
Go to the 2nd floor. Use the crank.
Go into the light room. Pour fuel into the light.
Wait.

Pick up the lamp from the bedroom table.
Go into the Shed. Take the spade.
OPTIONAL Go behind the Lighthouse. Dig the pile of dirt. Take the "caterpillar" medallion. Place it into the chest in your bedroom.
Go to the Three Tree area.
Turn around. Run into the Shed.
Go to the Three Tree area. Dig the pile of dirt. Pick up the key and the canister.
Go into the Lighthouse storage room. Fill the canister with fuel.
Go onto the 2nd floor. Use the crank.
Go into the light room. Pour fuel into the light.
Wait. The light stops spinning.
Go to the 2nd floor and use the crank.
Go into the light room.
Wait. The light turns off.
Go into the storage room and fill the canister with fuel.
Go into the light room. Pour fuel into the light.
Wait. The light turns off and stops spinning.
Go into the basement and fill the canister with fuel.
Go to the 2nd floor and use the crank.
Go into the light room. Pour fuel into the light.

Pick up the key on the bedroom table.
OPTIONAL Go on the Lighthouse balcony. Pick up the "moth" medallion. Place it into the chest in the bedroom. Open the chest. Take the shotgun and the shells.
Go into the Shed. Pick up the hammer, the nails, the boards and the ladder.
Go to your House. Place the ladder outside next to the bedroom window.
Climb onto the roof. Place 4 boards on the hole in your roof. Use nails on all 4 boards. Use the hammer on all 4 sets of nails.
Go inside your House. Pick up the key on the kitchen floor.
Go into the Lighthouse storage room. Pick up the lamp and the canister. Fill the canister with fuel.
Go to the 2nd floor. Use the crank.
Go into the light room. Pour fuel into the light.
Go to the 2nd floor.
POSSIBLE ENDING ONE. If you have the shotgun and if you so choose - shoot the creature. You get the Judgement Ending.
Otherwise--
Run into the basement.

This map is very rough and the true length of corridors can vary wildly but the general structure is correct.

Avoid the creature. It's advisable not to use the lamp as it may attract the creature. Follow the yellow path on the map. Fall into the hole at the end.

You will appear in an underworld of some kind. Walk through it and enter the Temple.

Pick up all the medallions and insert them into the chest. You have to pull the lever closest to you at first but after that you can access the medallions in any order you want.

-//-

Row, row, row your boat.
Row, row, row your boat.

Go into the bedroom of your House.

-//-

You can't use/stand on the stairs.
Go to the 2nd floor of the Lighthouse and cut the rope under the crank.
Go to the 1st floor and eat the 3 bags of grain.
Go into the basement.

-//-

Chase after the man, if you want.
Go behind the Lighthouse.

-//-

Walk forward. Enter the door.

-//-

Go to the 2nd floor of the Lighthouse.
Go to the storage room.

POSSIBLE ENDING TWO. Go to the light room. You get The Hanged Man Ending.
Otherwise--

Go into the basement.
Go to the end of the underground area, same as you did last time.

POSSIBLE ENDING THREE. You get The Devil Ending.