The subway is a way to get places more quickly, and without getting lost, and also has no Astronauts. The only special material you need are Ice and Light or Mini Lights, so a subway is quite feasible in either survival mode or creative mode.
I play in creative mode. Some time after I had built a pretty good base, I accidentally threw away my graphite and wanted it back. Checking the Assembler recipes, I saw that I could make graphite from Moon Bark, which must be obtained from Colorwood trees (because it is not provided for you).
Colorwood trees are pretty rare on this moon (I had left all the options set to the default center position) so I had to look pretty far to find one.
I created the Subway so I could search for the Colorwood tree without getting lost, and so I'd have a way to get back to base in the future without encountering too many Astronauts.
Later, surface-level lights were added to mark the position of the Subway, giving me a way to re-gain my bearings when walking across the open, undeveloped surface.
As was handily pointed out by user OrigamiDragons, you can walk about 50% faster on Ice, so I have changed all the floors of the subway's corridors to ice. This makes it the fastest way to get anywhere that's more than a superblock away, even if you count the time to go down the stairs at the entrance and up stairs at the exit.
Here is the current layout of the Subway. East is at the top:
Common Design Elements
The Subway has two main tunnels, one above the other, running strictly east to west and located at -7 and -23 (depth in blocks below the level of the ice surface). These are connected directly to each other at several points with side staircases, and many of the station exits also provide a way to get from -7 to -23. Near the middle of my moon there is a third level at -39. (The purpose of these multiple levels is to connect with rooms and other things that I have created at various different depths.)
As mentioned above, the corridors have Ice floors because that lets you go 50% faster. Combined with the extra speed from equipping with an Energy Orb, the speed is so fast that it's pretty much impossible to see when you're about to reach the stairs that branch off to the exits, so I've marked the exits with two or three extra Light blocks, or some other really clear marker. I usually also add identifying color Materials (each station has an identifying block, see the subway map above) and a block of Blue Stone showing which way goes back to my home base. (I wrote a bit more about such tricks in my blog Signs in a Signless Game).
Most stations have one or more exits consisting of ordinary diagonal staircase ending in a "bunker" type structure that allows me to enter but blocks Astronauts (see my Astronaut Wrangling article). Most stations have a specific color, and the -7 tunnel and the -23 tunnel have separate stairs to the exit. Sometimes there are two or three bunkers, and sometimes a single bunker connects to all the stairs.
There is also a surface path marked by a uniform row of Light blocks spaced 4 units apart, and most of this is cut through hills whenever necessary so that I can traverse it as easily as on level ground. You can see this in many of the photos below.
Stations - East End
Most of the east end is from my search for Colorwood trees, so it's just bunkers with little else of interest. The cooler projects are in the west end, see below.
Currently the eastern end of the line, Notch has just a single exit bunker, with the -7 tunnel ending in a simple staircase.
Kingsway station has magenta and Light towers.
The Peachtree exit incorporates a repurposed Brown_Mob blast pit.
This station has a southward surface spur connecting to a spot with some prominent craters.
- Aurice is named after a gold deposit under the ice
This is the "center" of my moon, and is just a little bit south from the original game spawn point
Stations - West End
After Base started to feel crowded, I began heading towards the west to do try out bigger ideas.
A long branch to the north connects to most of my Astronaut Wrangling test area.
This was the western end of the line when I started this blog, and connects to the immense Hollow Hill Project.
Westhill has a tall Molybdenum spire overlooking the west side of Hollow Hill to the northeast, and Castle Lake to the southwest.
My medieval castle and town project is described in the blog article User_blog:Mrob27/Molycastle.
There is a subway spur to a connecting loop linking about half of the towers in the city wall.