We'll need to go through Phthia to get the second Fragment of Love, and it's not gonna be easy.
Argolis
From here, leave the cave and call Pegasus with the harp and head to Attica.
Attica
The old man in the big house near the temple will tell you that the Nymph has gone to the Garden of the Hesperides, and to take the key that he gives you and go after her. Take the key.
From here, head to the left and go through the cave, then head to the right and battle Gaea. Wake him up with the ocarina, then get ready to fight. Gaea will throw rocks around, but if you stay on a higher ledge and keep striking with the sword, you'll be able to beat him. After you beat Gaea, you'll be able to head to Phthia.
Phthia
The slugs quickly move back and forth. They will be too low to hit, but you can use the fire from the Staff of Fennel to burn it. Otherwise, avoid them.
Head left when you arrive, then go downwards. From here, left and enter the door on the lower-left corner to use the fountain if you need it. After that, head up the nearby stairs and head left. Be ready to avoid enemies as well as the pits, then head left and go through the cave to enter another temple.
You'll meet Hephaestos. If you have 70 olives - which you should have - you'll be able to buy his sword. Buy it; Hephaestos' sword - the Divine Sword - has the power of Argus and is the strongest weapon of the game. It can shoot lightning forwards, but it can also drain your health when you do this unless you have the Bracelet of Power. Hephaestos will also tell you that there is something useful in the Garden of the Hesperides on the other side of the waterfalls. Be sure to get a password from Hephaestos, too.
From the temple, head right until you find an opening. The old man inside will give you some ambrosia to increase your maximum health, and if you talk to him again, he will tell you to see the witch Circe before going to Phrygia. After that, go back and make your way down the stairs and back to where you started. From there, head to the right. The man in the opening up the stairs as you make your way up will tell you that if you are looking for the Golden Apple, it will be guarded a huge dragon known as Ladon.
Head to the right and take out the Centaur with the lightning from the Divine Sword. The Centaur will go down in two hits, and you don't have to deal with the arrows or the Centaur bouncing around all over the place. From here, go right, jump up the platforms and walk into the waterfall.
Use the Crystal Ball halfway through the upper path to reveal a door. Go through the door in the next room now that you have the key, and you'll find a Nymph who has fled here after being found by the Graeae at Laconia. The Nymph will tell you that Helene has been taken across the sea to Crete, and you'll get a letter from Erinna as well as the second Fragment of Love. Take the Fragment, and you'll hear from Erinna.
Erinna will tell you that she loves you so much and that she will never belong to Hades, as you will come to save her. She will then tell you that according to Hades' servants, the entrance to Tartarus lies along the sea between Crete and Argolis.
From here, leave this area, then head right across the upper part of the cave and go through the right opening. Keep going, and you'll soon find yourself in the Garden of the Hesperides. The butterflies will bob and weave through the air and spray poisonous powder, but you can hit them from a distance if you know what you're doing. The plants will shoot fireballs at you, but you can block the shots with the shield and hit them with the lightning from the Divine Sword.
At the end, you'll face Ladon. Fire lightning from the Divine Sword at the head, and keep away from Ladon as it flies around, as it can be devastating at close range. Beating Ladon will get you the Golden Apple, which doubles your defense. This is one item you'll really want.
From here, enter the lower opening to the Garden and go through it to get back to Phthia. Back at Phthia, get back to Attica.
Back to Attica
From here, head back towards the temple, refill your health at the fountain, and save the game; you do not want to go through any of that ever again.