Here is the full list of all 20 Old School RuneScape achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Visit the General Stores in Lumbridge, Falador, Varrock, Edgeville, Rimmington, Al-kharid and Karamja (Musa point)
Catch a Tuna at Musa Point
Craft some Air Runes at the Air Altar
Equip a Mithril Scimitar
Pass through the Al-Kharid/Lumbridge gate without paying
Equip Fancy Boots or Fighting Boots from Stronghold of Security
Ride the canoe in Lumbridge
Complete a Clue Scroll
Complete the Vampyre Slayer quest
Complete the Demon Slayer Quest
Reach a total level of 100
Complete the Dragon Slayer quest
Reach Combat level 20
Enter the Wilderness
Chat clothing with Thessalia in Varrock
Use the Home Teleport Spell with any spellbook
Complete the Cook's Assistant quest
Visit Death's Domain
Complete the Tutorial
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