Here is a list of ALL dungeons currently available for lv10-14 twinks to enter freely (by either walking into or through the Timewalking dungeon queue). To access the dungeon queues for Chromie Time Classic dungeons, you need to enter the Cataclysm timeline. There are Timewalking events for every expansion up to Dragonflight, and the schedule is typically chronological outside of Turbulent Timeways.

The following mount drops can be obtained by level 10s in Timewalking - due to the level requirements to learn these mounts, you will have to level your twink in order to use them! Otherwise, chuck them in the bank and hope Blizzard fixes that.

If you managed to unlock the Campaign skip, and want to possibly lock yourself into receiving the bugged ilvl 252 loot from SL leveling dungeons, you can do Torghast when you do the campaign skip on a level 10. This is ill-advised unless you have no expectations to farm loot in Plaguefall, The Necrotic Wake, Mists of Tirna Scithe, or Halls of Atonement.