The Goddess' Towers are revealed via a scripted secret.
If you enter the screen when you have the right item, they show up.
I have been trying to come up with a good way to reveal all eight locations, but so far nothing feels right.
The Sleepy Thwomp was chosen because I didn't want to have a sideview section for just one screen.
You can boost your damage underwater.
I consider the Octogon fight in the Goddess' Tower one of the hardest in the quest.
This is because not only does he have double health and defense, but he regens too!
To enter the Secret Corridor, there are several requirements.
By defeating all 9 Mario Monsters, you meet the first of them.
Next, you must collect all 10 Shadow Shards.
Third, you have to obtain all 20 Secret Seashells and get the Fierce Diety's Sword from Seashell Mansion.
Fourth, you must finish the Trading Sequence.
Fifth, you must complete all 8 Siren's Keeps.
Sixth, you have to finish all 8 Goddess' Towers.
And last, you must visit the five fairies around the world.
Zol, the All-Consuming is a super-boss who shifts weaknesses and shows you what is needed to win.
He's unlocked by obtaining all 10 Zol Fragments.
Defeating him isn't required to get the best ending.
I liked the idea of a relatively weak-looking enemy being able to clean your clock.
Having the option set to heal immediately is very helpful here.
Also, the 4th Sword Technique can work wonders when he chooses that weakness.
I made it where you can dig to make the fight a bit easier.