Talk to Long-Bearded Viking named Sigurd in Fremennik... he'll tell you to find Antimatter Ore to craft into extremely powerful crystal that will warp you back to where you were. You must find Anima Wisp Energy in Wintertodt and Lunar Glyph in Waiko Isles to make a one time loop. Before departing talk to another NPC Sigmund Volkstragr (one with middle blond semi beard [just the RS Short Beard facial hair]). He will tell what his plan to one-time loop and warp and compression. Kharskai will appear to you, he tells why the world and time will change. After conversation, Kharskai and Sigurd will follow you to go to Spirit Garden.