Was the titan in the last episode of AOT S1 inside of the wall or on the other side? Also about walls origin First, is the titan really inside of the wall like being trapped in it or just doing his/its job (lol)? I thought it was on the other side ever since because I have seen many comments/texts using the word "inside" which is very confusing.

Also it was said so far in the anime (currently S2 E6), that walls are (possibly?) made of titans' "crystals" making it pretty much indestructible, so doesn't that mean that titans aren't neccessarily inside of the walls since it would make the plot point a very funny one.

I am also confused as to how the walls are said to be "indestructible" like titans' crystals except certain parts like "entrances/exits", but some titans are seen to be able to pretty much destroy wall parts that are said to be indestructible like how (the collosal titan destroyed some parts of it) not sure if it really did though? 

P.S. It's okay to spoil about the origin of the walls in your answers.
Please try and phrase your question so that it is not ambiguous. 

Also, explaining this will be a major spoiler. 

However, a few answers can be given. 


   1) Yes, that titan is inside the walls. 
 
 2) Yes, that titan created part of the wall with its hardened skin
 
 3) No, it is not trapped.
 
 4) The colossal titan can destroy a part of it, but not the whole wall.