Twilight Arbor Dungeon Track
It is on a timer but you can just unlock it permanently by doing the story mode. Story mode is pretty easy.
First, check the locked tracks if it tells “this track will be available in X weeks Y days.”
If it doesn’t say, then check which track is farthest off, then check the order of the Dungeon Tracks here: https://wiki.guildwars2.com/wiki/WvW_Reward_Track#Dungeon_tracks
Each track is available for two weeks, so you can count how far off the one youor need is.
To go from 0 to 500 tokens, you’ll need to complete the track twice, and get a little bit into the third time. Starting at zero in the reward tracks and only using potions, you’ll need 174 potions.
IMPORTANT: Remember to reselect the track when it finishes after 80 potions, the game autoselects a different track!
I’m sure you’re not alone, OP. Consider starting your own LFG for people to do story; it’s always convenient to have them unlocked.
Oh yes, try the dungeon story mode! I did it with one other player! Read up on the mechanics (I read the wiki) and it’s quite simple, might even possily be soloable!