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
Complete the Dragon Slayer quest
Equip Fancy Boots or Fighting Boots from Stronghold of Security
Enter the Wilderness
Complete the Vampyre Slayer quest
Complete the Demon Slayer Quest
Craft some Air Runes at the Air Altar
Pass through the Al-Kharid/Lumbridge gate without paying
Complete the Cook's Assistant quest
Equip a Mithril Scimitar
Complete a Clue Scroll
Ride the canoe in Lumbridge
Reach Combat level 20
Chat clothing with Thessalia in Varrock
Reach a total level of 100
Use the Home Teleport Spell with any spellbook
Visit Death's Domain
Complete the Tutorial
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