Final Fantasy/Temple of Fiends Walkthrough
The Temple of Fiends isn't very big, but there still exists the potential for some dangerous random encounters. Bones and Spiders are easy to get rid of. If you did buy HARM at Coneria, use it on the Ghouls. Grey Wolves and Werewolves are where the most trouble lies; both have lots of HP (around 70) and the Werewolf can poison you. You'll probably be inclined to run away, but if you're feeling brave, try SLEP on the wolves.
There's one optional destination here: the treasure room in the lower left. You'll pick up a Cabin, Heal Potion, and a Cap. The other rooms are locked for the time being. This is your call; the Cabin will be useful on the upcoming long hike to Pravoka, the other two items you can take or leave.
The reason you made this trip, of course, is the battle against Garland. Just march straight up to the center of the temple and take him on. Despite his cool hat, Garland is only a little worse than the strongest random monsters you've dealt with so far. He has around 100 HP and a moderately powerful attack. SLEP sometimes works on him, but you shouldn't need it. FIRE takes a lot out of him, and RUSE is very useful since it makes Garland miss on his attacks quite often. Just fight and heal as necessary and he'll go down.
Talk to Sara after the battle, and get warped back to Coneria. Talk to the king, and he'll build the bridge to the northeast that will enable you passage to the greater world. Buy some tents, pick up anything you intended to get but didn't, then start what will be a pretty long hike to the eastern town of Pravoka.