Illustrated Guide to the world of Spira (FFX and FFX-2)/Hidden Dungeons

There are 14 dungeons in the world of FFX and FFX2. Dungeons in Spira vary very little in style, most of them look like ancient stone temples with a hint of Ancient Egyptian stonework. Notable exceptions are Bevelle Cloister, Bevelle's underwater maze and the cave dungeons on Omega Ruins and the Den of Woe. Mt. Gagazet has a very unique cave dungeon with some parts submerged under water.

Bevelle - Bevelle Cloister Dungeon - Via Infinito
Can be explored only on Final Fantasy X-2. The dungeon is located at the right side of the Temple, 1st floor. It has several game goodies and solves some game story mysteries such as the whereabouts of Trema, the first leader of the New Yevon faction. Trema can be found on the 101st floor of the dungeon. Optional

Omega Ruins - Omega Dungeon
Can be explored only on Final Fantasy X. The dungeon is located in an unexplored part of Spira, at the Easternmost part of Spira's large continent. It has several game goodies. Optional

Calm Lands Gorge - Cave of the Stolen Fayth
Can be explored on both games. The dungeon is located in the northern part of the Calm Lands. It has several game goodies. Optional on FFX, mandatory on FFX2 plus the power up for Paine's special dressphere

Mushroom Rock - Den of Woe
Can be explored only on Final Fantasy X-2. Several game goodies. Optional.

Mi'hen - Hover Crash site Dungeon
Can be explored only on Final Fantasy X-2. The dungeon is located at the base of the Highroad bridges, where a hover crashes in chapter 3. It has several game goodies. Optional

Besaid - Wakka's Cave
The cave where Wakka goes on to look for his parent's sphere on Final Fantasy X-2. No goodies, Mandatory

Bevelle - Underwater dungeon - Via Purifico
Can be explored only on Final Fantasy X. It is a large underground sewer full of fiends. Tidus and the rest of the guardians are thrown there by Kinoc and Seymour. No game goodies. Mandatory

Gagazet Summit - Small Underwater/cave dungeon
Can be explored only on Final Fantasy X. No game goodies. Mandatory

Amazing Chocobo Dungeon
Can be explored only on Final Fantasy X-2. The dungeon is located at the back of Clasko's Chocobo Ranch in the Calm Lands. It has several game goodies. Optional

Thunder Plains - Tower Dungeon
Can be explored only on Final Fantasy X-2. The dungeon is located at the base of the 9th calibration tower, across the lake. It has several game goodies. Optional

Thunder Plains - Dragon Dungeon
Can be explored only on Final Fantasy X-2. The dungeon is located at the Southwest end of the plains. No game goodies. Mandatory

Bikanel Desert - Cactuar Dungeon
Can be explored only on Final Fantasy X-2. The dungeon is located in a cave on the back area of the Cactuar Nation. No game goodies. Optional

Zanarkand - Zanarkand Dungeon
Can be explored only on Final Fantasy X-2. No game goodies. Mandatory

Floating Ruins - Small dungeon
Can be explored only on Final Fantasy X-2. Some game goodies. Mandatory