I don't think there is a cave under cycling road in Pokemon heart gold or soul silver, are you sure you have the right name in your question? If you do mean heart gold, the next thing to do after going through cycling road is to go into fuchsia city, beat the gym leader, explore Pal Park, and take route 15, 14, 13, and 12 up to Lavender Town. Good luck!
in the ice cave
Up your moms @$$
on Pokemon diamond you can only trade whilst holding the kings rock where you get in wayward cave which is under the cycling road
you can find them on fridays in unoin cave
its beside the cave under cycling road you cant see the entrance cause its directly underneath the road if u know what i mean
The cave under the cycling bridge
a girl at the end of wayward cave under cycling road
There is no Unknown Cave!!
There is no Carmen Cave.
i don't know but i think one of the regis are in there
it is under the cycling bridge on the right side of mt.cornet when you go under the bridge go up until you go in it.
You can get Gible on Pokemon Diamond in the Wayward Cave hidden under Cycling Road in Route 206. You will need the HM move Strength to access the cave.
Cerulean Cave.
in the cave!
They are rarely found in Wayward Cave, the secret area under the Cycling Road.
Up your moms @$$
ice cave