Lewis and Clark did not spend an awful lot of time in Illinois. But they did visit the area now known as Dixie Fromm Briggs Nature Preserve. When they were there, they worked on some skills they would need on their grand voyage and some communication methods which they had worked out with Thomas Jefferson.
What follows is an actual transcript of a conversation between Meriwether Lewis and William Clark:
Lewis: Yo, Billy! Hey check this out. Jefferson sent me this whacked out coded message.
Clark: OK Meri, I'm coming on over to take a peek.
Lewis: Dude, don't call me "Meri." You know I hate that.
Clark: Dude, don't call me "Billy."
Lewis: Word.
Clark: So anyhow, what's the message say?
Lewis: I don't know. Its all in this freaked out kind of writing.
Clark: Lemme take a look.
Lewis: You ain't gonna be able to read it anyhow.
Clark [insulted]: Dude!
[Lewis shows Clark the coded message]
Lewis: I told you it ain't gonna make sense to you.
Clark [Gives the message back to Lewis and gets out paper and pencil]: Read it to me.
Lewis: OK: T, F, C, P, I . . .
Clark [writing with his left hand]: Keep them coming!
Lewis: T, K, Y, ampersand, G, V. Hey! I didn't know you was left handed.
Clark [smiles, switches to writing with his right hand]: Keep reading!
Lewis [not noticing Clark is writing with his right hand]: L, Z, h, i, B. [looks up, notices Clark has switched hands] Hey! Now you are writing with your right hand!
Clark: Yeah, well, when you were reading up on Native American customs, I was practicing so that I can do all skills ambidextrously.
Lewis: All skills? Even shooting.
Clark: Yep. Even shooting.
Lewis: Dang!
Clark: C'mon, lets complete this code so we can finish this mission before nightfall.
TFCPI TKY &G VL Z hi BQRRY KBET a LTPFR
EXQRY P WXA&ECF& FXX f QA&FNQ RGWR
20200312: Updated stage coords and puzzles for new placements.
20200314: Changed "Winter Friendly" attribute to "NOT Winter Friendly". Changed ciphertext from an image to, well, text. Updated dialog to match the new ciphertext.
20211110: Added a couple hints for S1. Removed "Recommended for kids" (don't that it's particularly applicable here) and "Takes < 1 hour" (maybe, maybe not).