What about the Door(that wasn't at the end of the tunnel)?

[fiondavhar]

No: HPFGUIDX 99809

--- In HPforGrownups at yahoogroups.com, "potioncat" <willsonkmom at m...> 
wrote:
> Jessica wrote:
>   Snape  was able to use the tunnel as a child and an adult, Lupin 
> uses it as  an adult, Harry, Hermione and Ron use it as well, so it 
> must be big  enough for at least an adult to use (although it may 
be 
> cramped). 
> > But I do think a stag would have a hard time using the tunnel if 
a 
> > person had to bend over to use it :))
> > 
> > Although there is no proof against an enchantment to prevent 
> > Transformed!Lupin from accessing the passageway. 
> > 
> 
> 
> Potioncat:
> The part that makes me think that the werewolf didn't normally get 
> into the tunnel (without Marauders' help) was Lupin's comment 
> that "had Snape gotten in the house, he would have met a full grown 
> werewolf."  (paraphrased)
> 
> I think everyone except James could have used  the tunnel, as an 
> amimagus.
> Potioncat

Bonny:

But they used to run about the grounds on nights that Lupin 
transformed - which means that they would have had to come back 
through the tunnel. 

"Soon we were leaving the Shreiking Shack and roaming the school 
grounds and village by night. Sirius and James transformed into such 
large animals, they were able to keep a werewolf in check."

   - PoA, pg 260, Canadian paperback edition.
I think the most likley scenario is simply that Lupin thought like an 
animal when he was transformed, and an animal likley wouldn't stop 
and rationalize to figure out how to get out of the house. He went 
pretty crazy according to PoA, though less so when the others were 
with him. He probably always had the physical ability to leave the 
shack, but not the rational ability. 

Bonny