Yep, Darth is correct that Asaechao is correct and that I edited the map.
The very first release of Frontier had the main spawn tunnel and also steps down to underneath the cannon. The steps were removed due to spawncamping zombies.
This meant that the only exit out of the spawn for the 2nd version, (and possibly the most known version) was through the big main tunnel. It comes to a T Junction. Right to the cannon, or straight on along the tunnel. It was zoned such that the junction everyone could go in, but nobody could place weapons, but the spawn tunnel was spawnkick zoned.
However, as it "wasn't obvious enough" that it was a spawn, the map was changed. Rings of colour were added on the walls of the tunnel to indicate where the spawn kick zone starts, and strips of colour along the walls and floor IN that zone.
Unfortunately (for you), I felt that the one exit from the spawn was far too spawncampy. So I re-added the stepped tunnel down to the cannon area, this meant it was harder to get kills than just sitting under the cannon placing TNT or mortars.
Now, I'm PRETTY sure that I made this exit 2 blocks from the floor, and so you cannot jump into it. But As a precaution, I added the colours for the zoned area.
The cannon and spawn tunnel entrances are pretty busy areas, so I also added the other exit which takes you closer to the middle of the map, and relatively high up on a wall to prevent spawncamping. But I made it pretty just to cover all bases. (Quite an ironic use of that phrase don't you think!)
I assume the tunnel you are talking about is the main spawn junction. I thought about making it stepped, but it would have had to be 2 higher than the floor, and generally would've been just as effective. Perhaps even less effective as the colour wouldn't have stood out as much.
However, I believe that the coloured exits and tunnels quite clearly indicate the spawn zone. Particularly, as both teams spawn in identical areas and must therefore see the style of where they spawn.
