This is called pathing
#Should be able to go from ramparts from prison depths
green sky
fossil bay
Man finds out that different routes exist
placid lava
Ik they do. but it just seems its wierd its the only one where you can't go to either of these biomes. ik its not required just seems like it'd be nice
fading grail
you can get to ramparts from corrupted prison at 1bc+
placid lava
you can get to ramparts from corrupted prison at 1bc+
you know what, i swore this was ossuary. I'm a dumbass. thanks
cosmic oyster
you know what, i swore this was ossuary. I'm a dumbass. thanks
You can delete this suggestion 
limpid violet
LOL
limpid quarry
Do you mean the other way round? If you could exit ramparts into prison depths, would break the game balances with scrolls, since you'd have an extra main biome before fighting the first boss. Assuming you must mean the other way round?
reef brook
Prison depths is entered from promenade or arboretum, and can lead to ossuary, morass, and I think ancient sewers at 1bc+
Corrupted prison is the alternative and is entered through toxic sewers. It can lead to ancient sewers and ramparts afaik
They function as a mid/extra stage between stage 2 and 3, ramparts is a stage 3 option so it wouldn’t add another main biome