some of my ideas. place name in brackets suggests where the event occurs.

1. Helping Escape for prince/princess/nobles/peoples from City (world map, on the road)
random quest occurs near by refugee's home city.

2. Learning Monster Language (both)
this might not be event but could relate to it.
some monsters are apparently Ethistos native, so why not learn their language ? (after defeating specific strongest mob/boss.)
once learned, player can have low chance to try interrogation if beat target monster till almost dead, and if successful, can get some important info.

3. Assassination (world map)
random but high chance of encounter to combat with hired (or brainwashed) assassin by shadow forces. after player gets reached rather higher levels. (seems unstoppable for shadows.)
always solo but higher level than player. and he/she tries to escape with teleport like ability in danger. and steals some consumables (foods, potions, magic gems, scrolls and wands) away. almost impossible to kill. 
reward should be only loot but precious one.

4. Magical Gem Vein (both)
in world map, player can expect natural source of magic gems.
in dungeon, some wall could contain them.
needs special tool to dig it out. (maybe unbreakable adamantite pickaxe ?)
but only if the player was fighter type (yes, muscle talks) and not elf (they already have better innate ability), this event could be triggered.

5. Secret Deep Dungeon Levels (dungeon)
some vault levels which is completely hidden and can't be found in normal way.
only after some condition met, player can start searching entrance.
it hides important things/secrets but optional. (good for achievement thingy.)
small forgotten cave is ideal for candidate. 
additional 27 to 57 levels would suit for it's importance. (usually player can access only 3 levels)
with going deeper, becomes harder. no magical merchant. some fallen boss reappears in stronger shape.

6. Bard event (world map)
this needs implementation of new ancient strange tome or scrolls which is worthless in itself.
and player can't decipher them. 
if player could meet traveling bard, he/she can ask for related old song when holding target legacy.
bards are just knowing the ancient lyrics and songs, so they provide only hints.
combination with old druid legends might be logically good. which can be heard from chief druid after getting hint phrase.

7. Stone Circle (world map)
if found, even fighter can have a chance to get spells, mana point or arcane thread. but its limited to utility spells and minimum number. (like detect trap and phantom presence.)
with this implementation, there will be meaning for fighter to get mana point when leveling. 
for casters,  no mana point nor thread chance. so its not that big bonus but precious chance to raise utility spells.
in its powerful nature, this event should be rarest (but can start in early stage) and occur only several times.

8. Eagle of Legend (both)
yes, its HUGE. and player can ride on. best transport for end game. (fastest and no random encount.)
needs to decipher ancient legends and what's not to find and revive him.
for this event, ancient tome mystery and bard event become important.
apart from legend part, player needs special artifact to call the eagle.