Nino Island

Nino Island is a very small island that is home to Ruminoa City. Heavily armed with various weapons, it's main purpose is to seal off the ruins from pirates. Entry to the ruins itself is controlled by the Guildmaster. Like in the Yosyonke Gallery at Calinca, you can also take the Diggers Exam by talking to the receptionist (the twin sister of the girl who does the same thing in the Gallery).

Location
Nino Island is composed of 4 levels with level B4 being the ruins itself.

Level B1: Reached by taking the elevator with the "up" sign. You'll first come to a room which contains the broken-down Parabola Gun and a ladder leads to the roof. After the encounter with Glyde using the Parabola Gun, this area is sealed off

Level B2: The Hangar. There are three doors and two elevators here. Roll and Data can be found here when the island is under attack. Doors one and two lead to cannons and turrets that help fend off pirates during the attack while the third door is  where the flutter is docked and where one of Glyde's ships tried to dock into.

Level B3: Ruminoa City. Reached by taking the elevator with the down sign. Places to go to (starting from the left) are the Guildmaster's Office, a bar, the Guildmaster's Room, a residential home, an item shop and a weapons store. The entrance to the ruins is located in the center.

Level B4: The ruins itself. The entrance will only open up after Glyde and his base has been taken cared off.

Trivia

 * While not said in-game, Nino Island is presumably a man-made island.
 * When the Birdbots succeed in breaking down the doors, the Guildmaster is seen activating the self-destruct button without any hesitation, effectively killing himself, the pirates and Megaman and the other citizens.