Tin Tower

From Pokémon HeartGold & SoulSilver Wiki

Tin Tower

At the first floor there will be a bald guy that won't let you go up until you have the Rainbow Feather. In SoulSilver you get the Rainbow Feather from an old man in Pewter City (he is to the right of the PokeMart). Once you have the Rainbow Feather he will stop you and the Rainbow Feather will fly and shine and he will let you pass.

Ho-oh

Ho-oh is at Lv. 45 in HeartGold and Lv. 70 in SoulSilver. If you defeat Ho-oh instead of catching it, it will give you 1414 Exp in HeartGold and 2200 Exp in SoulSilver.