Pokemon Heart Gold and Soul Silver - Walkthrough - Returning To Olivine City Pokemon Heart Gold and Soul Silver: Walkthrough - Returning To Olivine City
OLIVINE CITY:

Once you arrive here, head for the LIGHTHOUSE.

OLIVINE LIGHTHOUSE:

Take the elevator to quickly reach the top. Go and speak to JASMINE, and the Pokemon will become better after you hand her the SECRETPOTION you got from CIANWOOD CITY.

Now, get back in the elevator and head out into the city.

OLIVINE CITY:

You will get a call from BAOBA. The SAFARI ZONE, or the Gate to it, is now open! Check the SIDEQUESTS section for more.

With that done, you can head to the GYM. Make all necessary preparations and then move out!
This walkthrough was written by MKaykitkats, used with permission.