Started at the fifth anniversary, these are all activated every year (so far). Before then there were various special events that haven’t been repeated. The ones worth doing are: Sixth (experience potion), Ninth (Plane of Knowledge gate) - for tanks/melees/hybrids, Tenth (title, 10 x experience potions, mount), and possibly the 11th/12th, for factions and augmentations, depending on the quality of gear. The 12th solo augmentation is ok.
The reward is a Staff of Endless Adventure, which is a firework clickie.
There is a quest NPC in each of the old starting towns (not sure about Crescent Reach), plus one in the Plane of Knowledge: Skrasa Ka’rok, a sarnak in an anniversary booth on the evil side. When you accept the quest, you are given a Collection Bag and a Collector’s Cheat Sheet; you have to collect ten items, each called a “Collector’s XXX”. Answers given in the order I collected them:
To travel, I used PoK stones and origin, with the exceptions of Sol A and South Karana, where I used Guild Hall ports. For difficulty (for low level players), spectres were the highest, then the old sharks, followed by the gnolls - then everything else.
There are two gargoyles in Mistmoore right at the entrance; otherwise, you’ll want to use the map to find the secret entrance in the graveyard, and travel to the gargoyle room from there.
In the Ocean of Tears, old sharks can be found around the ancient cyclops island (second west from Sister Isle).
Once you have them all, combine the bag and hand in.
Reward is a Ceremonial Elixir of Scholarship, a one time only experience potion with ten charges (meaning, you can’t repeat the quest to get more). You can’t repeat this quest, it’s just once per character. There are two starter NPCs for this quest; one outside the elven outpost in Firiona Vie, and the other by the port in location in the Dreadlands. Because of it’s location, the Dreadlands quest giver, Sarvil Amberstone, is the easiest to start with, and you can move from there to Burning Woods, Frontier Mountains and back to the Dreadlands, then on to Firiona Vie and the Lake of Ill Omen, if you want to do them all in one quick sequence.
This quest is very similar to the Fifth Anniversary, in that you are given a Collection Bag and a set of clues. Most of the zones required are a single step away from the Cabilis stone, although the Firiona Vie stone gives better access to several others: the Dreadlands mob area, through to Burning Woods, Frontier Mountains and to the Firiona Vie zone itself; and the Overthere stone to the Overthere. The Dreadlands quest giver is best reached from the Guild Hall port.
There’s a trick to this quest: the items mainly drop from wanderers, not from static camps; see my notes below.
I spent over two levels at 49 in Burning Woods, around the crater; then I got one from a roamer in the SW. The Warsliks Woods drop came from a spirit caller somewhere in the woods, after clearing the fort around a dozen times. The Firiona Vie drop came at the drolvarg building, SW of the elven camp in the far east. The tump stump came from a wandering giant, after clearing the fort several times.
Bloodgills, drachnids and hornets are probably the highest levels, around 35-40 (wasps more like 40-46).
Pub Crawl Brasse in the Plane of Knowledge; level 75+, rewards a 30 minute reuse, fast cast port to Plane of Knowledge. See guide here: Brasse’s Stein
Most (recent) missions require level 100, and give a mission specific reward as well as currency (Commemorative Coins) that can be spent at a jubilant merchant in Plane of Knowledge. There should also be a mission and raid for the Plane of War, which may or may not be restricted to the Anniversary time. There is an achievement given for each year’s anniversary tasks; 13th, 15th and 16th have an additional achivement for completing the bonus stage in each task.
The merchant sells a large bag, a mount, food, fireworks, and various buff clickies.