One of the Ace Trainers in the cave says there is, but nothing yet. From the sound of it, it may be the site of a future Keldeo event.
NO
There is no Legendary Pokémon available in Challenger's Cave.
There is no legendary Pokemon in Challenger's Cave, only one person who said one used to live there.
There is no legendary Pokemon in Challenger's Cave. One NPC mentions that one Pokemon was raised there. It is most likely to be Keldeo, but it does not live there any more.
No, there are no Legendary Pokémon in Challenger's Cave.
In Challenger's Cave B1F and Challenger's Cave B2F.
You can get it in Challenger's cave
Challenger's cave
Whilst a trainer in Challengers Cave does say there is a legendary Pokemon there, there is in fact no legendary Pokemon in the cave.
Reshiram, Tornadus, Kyurem, Landorus, and I think that is all. But they DO say that there is a legendary Pokemon in a cave on Route 9. I will uupdate answer as soon as I find out.
If you are talking about Pokemon Black Version 2, then go to Mistrolen Cave
On the floor in Route 9 and Chargestone CaveMay appear in Dustclouds in Wellspring Cave, Chargestone Cave, Mistralton Cave, Challenger's Cave, Twist Mountain, Victory Road, Giant ChasmNote that in Pokemon Black you can also buy one at Black City.