Hydrophobe

Hydrophobe began as a sort of spiritual successor to a Republic commando map, Depot. The map consisted of two main "base" areas that were separated, the only passages between them was to take a tunnel system, or a series of ramps that led between the two.

http://img844.imageshack.us/i/reach9397373full.jpg/
http://img9.imageshack.us/i/reach9401362full.jpg/

Above, you see the tunnel that connects the two areas. from above it makes a sort of Z shape, if the vertical section of the Z were perfectly vertical.
_
|_
Like that.
In gametypes like stockpile objectives will spawn in the center of the tunnel to draw people away from the high-ground advantage.

http://img88.imageshack.us/i/reach9391774full.jpg/

Here we see the ramps that connect the two areas. They come together to form a platform on top of the tunnel, allowing for two-leveled conflict, without either level being fully aware of the other.

Shortly after completing this fairly accurate remake, I found that it was just too boring, so I expanded upwards.
http://img560.imageshack.us/i/reach9391763full.jpg/
http://img560.imageshack.us/i/reach9391799full.jpg/

After expanding upwards, I found that the bottom level was extremely empty. It was then that I decided to move it from the quarry, where it had been happily sitting, to the water just off the coast of the island. Several hours of writing down coordinates and transposing them later, Hydrophobe finally had its hydro, and its name.
http://img809.imageshack.us/i/reach9400491full.jpg/
http://img139.imageshack.us/i/reach9400508full.jpg/
http://img251.imageshack.us/i/reach9401357full.jpg/

A level of tower 2-story and tower-talls on top of the newly formed area really brought this map to life, not totaling 4 or 5 levels of combat space. What had started as a Depot remake now felt more like a callback to Prisoner (Halo:CE) or Lockout/Blackout (Halo 2/Halo 3).

Capture the flag and assault games soon turned into three story jumps off bases into the water, then danger-filled climbs to the top of the map. Headhunters found themselves holding out at high points, only to have to drop down out of safety or run across the map to cash their prizes. Oh yeah, and Elite slayer was tons of fun too.

http://img163.imageshack.us/i/reach9397468full.jpg/
http://img404.imageshack.us/i/reach9391775full.jpg/
http://img191.imageshack.us/i/reach9391776full.jpg/
http://img577.imageshack.us/i/reach9400510full.jpg/