Legacy of the Dragonborn Museum, full stop. I can't play without it any more. It gives you a massive museum in Solitude, with a living space and QoL features, a shitton of quests and new areas, and includes Moonpath to Elsweyr in it - amongst a bunch of OTHER mods as well! It is a MASSIVE mod that took the author literally years to finish, but it's done. There's a version for the special edition, too. I can't recommend it (and all the MANY mods it supports) enough!