Spelunky

NOTE: THIS IS NOT A FULL SOLUTION, simply a collection of tips meant to help progress towards this achievement.
WILL BE UPDATING SPORADICALLY AS NEW THINGS ARE DISCOVERED.

Journal log entries are made whenever you encounter a new place, item, enemy, or trap. This achievement should pop naturally fairly soon but here's a few tips for those struggling:

* Try new things! Buy a new upgrade from the store, use a different tactic on an enemy, try doing something you normally wouldn't! (perhaps sacrificing a golden idol to Kali, the god of death?)

* Kill everything you meet! Failing that, let it kill you! Being killed by an enemy or trap is sometimes the only way to get them into your journal.

* Use all the different kinds of items, and try out that new loot from that big bad monster you just killed! Alien queen drop a shiny looking toy? USE IT! or at least pick it up before you die so it get's recorded!

- secret levels-

WORM LEVEL* Throwing a damsel/dude/pug onto one of the sticky orange blobs you see in the jungle / ice caves areas will summon a giant worm! Stay on the blob with your damsel (fairly high up on the blob) and the worm will eat you both, taking you to a new Worm level!
PLEASE NOTE: This level is populated by enemies from whichever area you've recently left! So if you want to fight bats instead of yetis and aliens, enter from the jungle!

HAUNTED CASTLE* Sometimes on the Jungle level one will receive the event text "The dead are restless...". When seeing this text, keep an eye out for a grave marked by a crown, with a crowned skull visible below out. Bombing out the square below the skull will reveal an entrance to the Haunted Castle!

ALIEN MOTHERSHIP * When you get the "fourth of july" message when entering the end of the Ice Caves, you'll notice a large alien structure on the map, which assuming you have the right gear, can be climbed and infiltrated to reach the Alien Mothership level!

GOLDEN CITY * This is a multi-step quest and quite a pain if you're unprepared for the task!
- First step is to combine the golden key with the locked chest in the Mines area. it'll always appear on either 2-2 or 2-3.
- Now you'll take your new Udjat Eye into the jungle, and again on 2-2 or 2-3 pay attention to the eye's icon as you traverse the cave. Once it starts flashing you're near the black market, the faster it blinks the closer you are! Use some bombs or your leftover mattock to unearth the entrance, and we can move on to step three!
- Once in the black market you'll want to find the Ankh, 2nd level to the far right. You'll need a cool 50000 to purchase it, or you could always risk stealing it.
- With your new Ankh equipped, adventure in the Ice Caves until you find a giant blue stone head. You really can't miss it, just be sure you're exploring the whole of every level so you don't miss it. Once located, simply stand on or near the statue and kill yourself!
- Once dead, your Ankh kicks in, transporting you inside the statue where you'll receive the Hedjet. Now the hard part. Make it the rest of the way to the Temple, and find and kill an Anubis.
- New staff in hand, simply seek out the golden door somewhere in the temple area, and the door will unlock!


HELL * UNCOMFIRMED
once in the golden city one can find the Necronomicon. Golden city is all one stage so you won't miss it. Picking up the book will spawn Anubis II.
The difference being this one chases you and is near constantly spawning red skeletons to try to kill you. Once Anubis II has been defeated you can make your way to Olmec, take HIM out, and you should be able to see a doorway to the Hell area somewhere above the lake of lava. AGAIN, THIS IS UNCOMFIRMED AS OF TIME OF WRITING.

You add things to your journal by either killing enemies or picking up items. The best way to do this, since you'll be replaying this game over and over in order to beat it, is to waste your money on stuff you don't really want as long as you've never bought it before, and taking risks to kill tougher enemies just to get them in your journal so you don't have to worry about them on future journeys.

I would post a list but, really, pick up every item and kill every type of enemy and this will unlock in the Jungle or possibly Ice Caves. There is nothing rare or hidden needed to be found to hit 50%.