Rumors for your megadungeon ... before it's built

I've come up with a simple idea for creating rumors about that huge dungeon for your D&D campaign.  The best thing about it is, you don't even have to start writing the dungeon before you start feeding rumors to your players.  You don't know whether they're true or false--and it doesn't matter.  Once you actually create the dungeon, you can verify those rumors.

I'm describing how to apply the process for the blue basic rulebook from 1979, but this method is easily ported to any edition.  First, you need some wandering monster tables and magic item charts--either the original charts from Holmes, some specific tables you've written, or even my expanded Holmes wandering monster charts. 

Next, plug those results into some sentences that will spark players' imaginations (or appeal to their greed).  Something like this:

1. The [random monster]s are allied with/at war with the [other random monster]s.
2. Beware the fearsome/wily/hideous [random color*] [random monster]!
3.  The [same color] [same monster] is a gem/statue/painting of incalculable value.
4. The [same color] [same monster] is a powerful [magic item] of [spell effect].
5. The [random monster]s worship the [other random monster] as a god.
6. The [random monster]s love/hate [random character class**].
7. The [random monster]s will sacrifice any [character class] they meet.
8. The [random monster]s value copper/silver/gold/platinum more than any other metal.
9. Iron/gold/silver is poisonous to [random monster]s.
10. The singing/laughing/mocking [random monster] has a [magic item].

Here's how the table might look after filling in the blanks:

1. The dragon is allied with/at war with the wraiths.
2. Beware the fearsome/wily/hideous red wight!
3.  The red wight is a gem/statue/painting of incalculable value.
4. The red wight is a powerful potion of purification.
5. The doppelgangers worship the troglodyte as a god.
6. The rogues love/hate magic users.
7. The vampires will sacrifice/worship any fighting-man they meet.
8. The giant ants value copper/silver/gold/platinum more than any other metal.
9. Iron/gold/silver is poisonous to giant rats.
10. The singing/laughing/mocking patriarch has a cursed scroll. 

There you go--ten rumors to intrigue adventurers and lure explorers into your labyrinth.  It's up to you as the designer to figure out how they mesh with the actual adventure.  You could use these tidbits as idea seeds to start designing your dungeon, or you could just rely on the dice to tell you what's in those chambers and determine the truth at the same time as your players.  Happy adventuring!  

*Color table:

1.  red
2. orange
3. yellow
4. green
5. blue
6. purple
7. black
8. brown
9. white
10. invisible

**Character class table:

1. fighting-man
2. magic-user
3. cleric
4. thief
5. dwarf
6. elf
7. halfling
8. hireling