Hi again, yes another mob trap, except this one is a little more down to earth :). i built this trap legit in sp, it took around 2 weeks of 1-2 hours a day to collect all the neccessary resources, design and build the whole thing. i call it 'efficient' firstly because it has a decent capacity, an average sized dual tower setup has a good 2500 spawnable blocks (as much as a 50x50 flat trap) but can produce 4 times the number of items. just for reference, a single tower can be built on advanced maps in about 2-3 hours. by advanced i mean to say that a majority of caves have been explored and you have a decently sized stockpile of cobblestone. now, although it is labeled as 'efficient' it does require a significant amount of work in order to build successfully, the difference is that, because of the speed at which it kills the monsters, it will take much longer to reach it's item/hour limit, meaning in turn that you can clear caves progressively and continue to see increasing itemrates for longer.

materials required for 1 tower:
- 3 single chests full of cobblestone (or whatever you want to make it from)
- 15 stacks of logs
- a lava source
- at least 2 buckets though it is recommended you have more
- 3 stacks or so of glass (optional, glass is for aesthetics only)
- free time
- an attention span (the tut vid is reeaaallly long :)

I recommend that you have about 11 buckets, as this will allow you to fetch all the lava required for the grinder in just 2 trips, though this is not strictly necessary i do recommend you make a few extras :)

here is a rather lengthy video tutorial/step by step:
http://www.youtube.com/watch?v=YVXAnj1S4eg

and here is a tour of my trap with some views of the spawn floors etc:
http://www.youtube.com/watch?v=n01eE0ipBGQ

If you like my creations then please do drop a like, it really encourages me to keep building stuff like this :)

enjoy :)