Doing a 2Man/6Hero full clear of Fissure of Woe for the first time (for either of us, so we were taking it very carefully)...and after 6 hours discovering that the Tower Mage was stuck in the spider cave and wouldn't go and open the Tower of Strength. Then trawling the GWGuru forums/google for an hour and a half, and discovering that we could lure that mage back out of the cave to his normal place using minions to fix him, so we finally finished FoW after 8 hours.
Doing solo A/Me runs through the first 1.5 levels of ToPK when SF wasn't permanently maintainable and before they nerfed damage done while using it.
Finally getting an E/Me sliver armor raptor farming build working for the "Farewell to Gaile" weekend, and earning enough that weekend to buy my second set of elite armor. Then hanging on to Saurian Bones just in case the collector for them from that festival came back in another celebration. I've still got about 2 stacks.
Doing the epic-to-me chain vanquish Solo+Hero/Hench from Temple of the Ages through to Yak's Bend, hitting all areas in between - and discovering that the Materials Crafter guys were also merchants so I could sell stuff every 2-3 maps. And the frustration of spending 45 minutes running in circles at Anvil Rock trying to find that ONE LAST minotaur patrol (everything else was dead), just to discover they'd been running in the same direction I was that whole time, so we'd been circling each other.
Finding the Falls the first time...
Stumbling across Maguuma Stade while vanquishing the adjacent area, having never known it existed prior to then.
Making 6k vanquishing the two maps prior to Majesty's Rest (from Temple of the Ages, solo+hero/hench)...and then spending it *all* at the shrine next to the bridge in Majesty's Rest to get rid of death penalties incurred from Rotscale and his pals, because I was in no way, shape or form prepared for that fight. It was the first time I'd been in that map...and holy crap it was nasty if your build/heroes were not tailored for it!
Pugging the Ring of Fire mission, and failing it several times - each time due to those fire-spitting spiders around the so-called "easier" way through. Finally succeeding by NOT following the Vizier's advice to take the back way, and instead going for the full frontal assault.