This location is not accessible on disc 4
While climbing the cranes and whatnot upon first entering FH, head to the lower level and speak with the Master Fisherman. Tell him you don't know what he's talking about to get a copy of Occult Fan III, and honor his requests to eventually receive a Megalixir.
Your first required task here is to visit the mayor. His residence is at the center of the large solar panel area. After speaking to him, Galbadian soldiers will attack on the way back. You can also find Martine, the former headmaster of Galbadia Garden, to the right of the Mayor's residence. (If you play Cards with him, you can win a full set of level 7 boss Cards. He'll also have your Ifrit Card later in the game if you lose it to Rinoa's father.) While you're at it, play Mayor Dobe to win the Quezacotl Card.
Once you reach the train station, you'll fight a weakened BGH251F2. Once it is defeated, Selphie's team will rejoin Squall's, and you'll have all six party members once again.
After the fight, there are a number of conversations that open up. Speak to the Fisherkid at the docks a few times to see his antics. Once he runs out of things to say, return to the Master Fisherman (assuming you spoke to him earlier). He'll tell you to meet him at the inn (i.e., the hotel). He'll give you a history lesson about Esthar, FH, and Mayor Dobe. Continue listening after he's done and follow him as he heads to the docks, speaking with various residents along the way. Keep at it long enough and you'll get a Megalixir for your troubles. Once the Master Fisherman leaves, you'll also be able to find a Full-life Draw point where he was originally sitting.
There is another small side quest of note here. You may have spoken to the left-hand cafeteria lady in Balamb Garden at some point. If you listen to her whole story, she will tell you about her son that left a year ago. One of the residents at the train station after the fight will talk about leaving Balamb and worrying his parents—if you've spoken to the cafeteria lady, you can tell him to head to Balamb Garden and see her. There's no tangible reward for doing this, however.
On disc 3, you'll return here with Squall and Rinoa. Fortunately, you don't have to make the entire slow walk to the train tracks. This will lead to a cutscene that eventually ends at the end of the bridge on the Esthar continent. As an interesting wrinkle, Edea will join the party at this point, too.
Once you have the Ragnarok, you'll be able to land directly on the solar array, which will save a lot of travel time.
If the Queen of Cards comes to Fishermans Horizon, you'll find her on the train tracks above the solar array. She'll usually head to the Presidential Palace in Esthar from here, but may also leave for Centra (Winhill) or Dollet. If you gave her the Sacred Card, the mayor's wife will have the created Irvine Card.
Your first required task here is to visit the mayor. His residence is at the center of the large solar panel area. After speaking to him, Galbadian soldiers will attack on the way back. You can also find Martine, the former headmaster of Galbadia Garden, to the right of the Mayor's residence. (If you play Cards with him, you can win a full set of level 7 boss Cards. He'll also have your Ifrit Card later in the game if you lose it to Rinoa's father.) While you're at it, play Mayor Dobe to win the Quezacotl Card.
Once you reach the train station, you'll fight a weakened BGH251F2. Once it is defeated, Selphie's team will rejoin Squall's, and you'll have all six party members once again.
After the fight, there are a number of conversations that open up. Speak to the Fisherkid at the docks a few times to see his antics. Once he runs out of things to say, return to the Master Fisherman (assuming you spoke to him earlier). He'll tell you to meet him at the inn (i.e., the hotel). He'll give you a history lesson about Esthar, FH, and Mayor Dobe. Continue listening after he's done and follow him as he heads to the docks, speaking with various residents along the way. Keep at it long enough and you'll get a Megalixir for your troubles. Once the Master Fisherman leaves, you'll also be able to find a Full-life Draw point where he was originally sitting.
There is another small side quest of note here. You may have spoken to the left-hand cafeteria lady in Balamb Garden at some point. If you listen to her whole story, she will tell you about her son that left a year ago. One of the residents at the train station after the fight will talk about leaving Balamb and worrying his parents—if you've spoken to the cafeteria lady, you can tell him to head to Balamb Garden and see her. There's no tangible reward for doing this, however.
On disc 3, you'll return here with Squall and Rinoa. Fortunately, you don't have to make the entire slow walk to the train tracks. This will lead to a cutscene that eventually ends at the end of the bridge on the Esthar continent. As an interesting wrinkle, Edea will join the party at this point, too.
Once you have the Ragnarok, you'll be able to land directly on the solar array, which will save a lot of travel time.
If the Queen of Cards comes to Fishermans Horizon, you'll find her on the train tracks above the solar array. She'll usually head to the Presidential Palace in Esthar from here, but may also leave for Centra (Winhill) or Dollet. If you gave her the Sacred Card, the mayor's wife will have the created Irvine Card.