In the beginning of UO there was a program that allowed players to enter coordinates and teleport to that location, provided it was not blocked. This resulted in players gaining access to many restricted locations & called attention to Devs. Program functionality was blocked soon after. Some of the rarest runes of this kind were handed down over +20yrs to friends as their original owners quit the game. Very few remain.
Some runes resulted from early telestorming. Players found themselves moved to bizarre locations & marked. Other runes were results of game glitches such as the 1st Blackrock/Armageddon spell event. At this events release, a player w mined blackrock could say the spell w 1 of several outcomes (blowing urself up entirely being one). Another possible outcome was being blown backwards (opposite from one’s facing direction) randomly between 6-12 spaces. If a player positioned themselves w their back to a wall, mountain, water, or any other impasse... the mechanic would relocate them to the nearest available spot up to roughly 15 tiles away. This was caught by Devs & removed in abt 7-10 days when players started posting abt how others were using this to enter private keeps & castles by blowing themselves thru walls on thief chars to stealing items. Likewise, it was used w/o nefarious intent to access areas & mark runes. Few of these runes remain as most players were unaware of the mechanic & most that knew weren’t explorers but thieves thus never set out to use it for anything other than profit.
The e-field/stone wall gate mechanic was commonly known and frequently used by many resulting in most of the rare locations runes found today. The lesser found runes of this type are city locations as said spells were blocked in guardzones.
Some runes came from events where the EMs created areas and forgot to block marking or simply missed small locations created outside the larger main areas. Some areas, such as Pirates Cove, the EMs never intended to block so players could return & enjoy the work they’d done. Others runes are results of defunct quests/discontinued storylines and global events.
There are far to many ways to create such areas to list them all & the list would be inadequate if attempted. These are just a few off the top. I’d like to thank those gaming explorers that set off to find & mark such locations w no ill intent, simply to show someone was here and noticed.... and say “hey, that’s pretty cool”.