Fel's Notes:
Some random loreposting to stall for time while I work on the next species entry, starting with some location-based things
In Underden, Mt. Ebott is an inactive volcano that's the centerpiece for Ebott National Park (located somewhere in the eastern US). Its a popular tourist spot for nature lovers and a good place for environmental science research, though visitors are encouraged not to get too close the mountain itself due to the many, many cases of people going missing around that area. The official explanation for this is that these people just got lost or fell down a hole or something, but the presence of a large metal fence surrounding the area close to the mountain with a bajillion warning signs does tend to raise a few questions. Many of the locals claim that the mountain itself is disappearing them, with one cooky old man even claiming that Mt. Ebott is a portal to the Underworld; that the demon king of the faeries is down there snatching anyone that gets too close and sacrificing them to pay a tithe to Hell. ...Yeah, most people just kinda ignore him lol. The Underground itself is just a giant network of caves and tunnels that stretches underneath the mountain, with multiple access points from the surface. The barrier disguises all of these entrances from the outside, so they look like normal ground/cliffs on the surface (very dangerous!)
The Snowdin area is the closest to the top of the mountain and has the most entrances, though none of them are particularly safe as you'd fall at least 30 feet straight down at the lowest one. As a result of all these little entrances, Snowdin Forest is the only area that gets enough light to support some coniferous trees, and also the only area that experiences seasons (a "snow" season and a "melt" season).
The Ruins (called the Ruined Catacombs by Marshall) is most easily accessible through the famous cave entrance that Chara/Frisk fall into, and has a moderate amount of light; enough to support some forms of plant life like vines, moss, lichen, and ferns. The pink-ish tint of the rock there is due to the unusual amount of iron in them.
The giant cavern where New Home is located (called the City of Stone by Marshall) only has one entrance on a cliff near the bottom of the mountain, but it's HUGE-- it lets a lot of sunlight into the cavern, but unfortunately doesn't help much in the form of plants due to the ground there being literally just rock. This is where most of the Underground's population can be found, and is the closest anyone can get to the barrier-- close enough to touch it, even.
Waterfall is technically the biggest region of the Underground, with tunnels stretching out for nearly a mile deep beneath the ground. The only notable entry point is the area where Ebott Park's river seems to just disappear, turning into a huge waterfall that continues flowing through Waterfall itself before dumping into Hotland and turning into steam. This river also has another starting point in Snowdin due to a small lake residing on the surface up there as well.
Hotland is the smallest area but also the deepest, extending down near Mt. Ebott's magma reservoir. It obviously doesn't have any plant life whatsoever and conditions there are extremely harsh, but somehow a not-insignificant portion of all monster species call it their home. It probably helps that a branch of the river was manually redirected into a cooler area of Hotland to at least grant some reliable access to water.
The Ruins are connected only to Snowdin, Snowdin is connected to the Ruins and Waterfall, Waterfall connects to Snowdin, Hotland, and New Home, and Hotland connected to Waterfall only before the pulley elevator system was established to allow easier access to New Home.
