Instructions
Enter the lighthouse located in the southeast corner of Olivine City. The lighthouse is full of Pokemon trainers you will have to fight. Use an assortment of your strongest Pokemon and bring plenty of healing items.
Use the stairs in the upper left corner of the first floor to ascend to the second floor.
Use the ladder on the right side of the second floor to climb to the third floor.
Use the ladder directly to the left of the entrance to the third floor to ascend to the fourth floor.
Exit the door on the right side of the fourth floor to enter the outside terrace of the lighthouse. Walk through the door in the middle of the lighthouse to proceed.
Use the ladder in the upper left corner to ascend to the next floor.
Use the ladder in the upper right corner to ascend to the top of the lighthouse, where you can speak to Jasmine.