its in viridain city in the kanto region. you will fight gary. (hes not the last boss, red is!)
the 16th gym leader is:Trainer Blue
Viridian city
yes, but first you have to beat blue (16th gym leader) and then you can find him in mt. silver cave
Sabrina
The fourth gym leader in Pokemon Soul Silver is in Ecruteak City.
in his gym
claire
get a Pokemon with a ressisstance
The 16th gym leader is Blue, then after that, you get the EARTH BADGE, and get a TM from him after, then you are able to use HM08. After you go to Mt. Silver, your going to fight Red, who is similar to Ash, his Pokemon are lv. 80-90. Blue is in Vermillion City in Kanto, the gym that is empty is where he is.
The first Gym Leader who is Falkner, the Violet City Gym Leader, he has a Pidgey and a Pidgeotto.
He is on Cinnabarr Island.
go to the Pokemon gym