The Tower,The Antenna, Obelisk and Tomb
Monumental M is one of the four man-made towers on the island and it lies at the center of the island. Around Monumental M, there are 4 statues placed at each wind direction and trapdoors have been set to keep large animals away from it.
Monumental M is approximately 15 meter high and has a obelisk shape with 2 points on the side. Above Monumental M it has a Isurugi Corporation logo and on the ground the foundation stone was written for reading 'Miina Isurugi - Requiscat in Pace', which is Latin for 'Miina Isuragi - Rest in Peace'. On the backside it has the coordinates of the island.
Makoto's Group had been searching for Monumental M since they saw it on the top of the Mountain. Aya Tokiwa and Miina Isurugi were the ones whom found it first. They headed toward it and uncovered a relic stuck on the ground. It accidently reactived one of Monumental M´s trapdoors and they fell into it. Akira's Group came and some of them also fell into the trap while searching for Makoto's Group. Thanks to Shirou Mariya they realised the trap and freed Morita's Group from the trapdoor´s pit. Yuki Sakuma and Shirou were theorizing that Monumental M could be used as a monument and also a landmark. It could be used as a guide from far away. The passengers of the plane could see it from far away.
Animal Battle arc
Propleopus, Smilodon and Titanis Walleri invaded the base and caused havoc among Akira's Group. Akira Sengoku devised a plan and used the trapdoor to lure Propleopus inside. After that they resumed the excavation around Monumental M. They found two more relics related to the first one they found near the trapdoor.
Daigo and Junichi were climbing on a tree when they saw Monumental M. The girls of Akira's Group caught them off guard and brought them back to base. During that night they escaped and they were caught again near Monumental M. After a while Akira managed to conviced them to take a party back to the Pyramid. Shirou was appointed leader as Akira's Pyramid Party left the base. After two weeks Akira's Pyramid Party returned with friends.
Failed Experiment arc
Shirou and Akira exchanged information of their findings. During Akira's absence the remaining members excavated the surrounding and Monumental M itself. All the trapdoors were uncovered and three more statues were found. They found coordinate set on the back of Monumental M. Shirou theoried a way how to get back home. At the trapdoors area a sleeping Chimera woke up from its hibernation sleep and attacked Akira's Group.
Tower of Death arc
Tower's real name was mentioned: "Monumental M".