The layout of the secret level is a bit visually messy, but the progression is fairly simple. To get to the second half of the map, you need to hit 3 switches and find 1 key. All of these are found to the right and left of where you start respectively (north and south on the map.)
The second half is nearly linear aside from some bonus pickups.

Respect for attempting it drunk :P

Thanks for the in depth comments! The levels were tested quite a bit as they were being built, but I only did a couple of them front to back with no saving. But I imagined that the maps would probably be quite possible to do without saving as I found easy ways of avoiding most things. Probably takes a while to find those tricks though, as you say :)

I was probably right to hide the secret level away like that. It was originally the last level before the boss. i made E1A6 "Unreal Estate" to replace it when I decided that it should be secret instead, so that the last level before the boss is something more "traditional".

Note: I played on the highest difficulty, with all the vanilla mechanics, free look, and without loading saves on death (using the lives system).

I'm on the last level. I had to play the campaign twice because I finally found the secret level and got stuck in it (I was drunk and lost about 15 lives not knowing where to go and gave up and started the whole campaign again).

About not having much room to move around, it may even be true in some cases, but I don't think it's a big deal to have more claustrophobic places. There are some set pieces that work really well, like the maze with the robots, or the part where you have to dance around the lava columns, and they only work because there's not a lot of room to move around. I like those more methodical parts, but it takes patience to find the best approach, and until the player understands that, they're probably going to get a little frustrated.

Overall, I think the levels are pretty solid and explore a lot of unique interactions.

Well, thank you for playing anyway. And feedback is always appreciated.

I do like long maps with theme changes myself, so that part is not likely to change in future maps thoguh.

I made it to the halfway point of map 3 and stopped playing. Maps never give you any room to move, even in city sections. Enemy placement is always simmetric (where one enemy type is placed at one corner of the room, you can be certain there will be another one of the same type at the other corner) and often times predictible, with mp40 guys placed at the deadends and behind the single tile windows. Maps get too long, change their theme midway through (like this city at the end of map2) and too often rely on using the automap (key doors on map 1 and labyrinth on map3). I see a lot of ideas here, but these maps are not that good yet.

Thanks. More coming... some day :P

These are really fun

High quality levels, good job.

Not sure where to go? Look for blue Oscuro walls.

Contains the following levels:
E1M1: Castle of Doubt
E1M2: Urban Sprawl
E1M3: Operation Night Owl
E1M4: More Than Bargained For
E1M5: A Short Vacation
E1M6: Unreal Estate
E1M7: Darian, Schmarian! (boss)
E1M8: Sinister Skyline (Secret)