Agent’s right. Your best bet is to consult gamefaqs – they have some helpful maps that I used to reach Ultima. It’s obvious that you can’t access the area easily, so make sure you can hold your own against the enemies there; some of them are very tough. You could easily run out of Phoenix Downs or the like. You don’t want to have to backtrack if you run out of supplies.
No problem. That site has all the maps the guide is missing.
Basically, if you want to play a perfect game and get everything you can at the earliest possible stage in the game, all you need is that site and the bradygames guide.