Go In and Out the Willow was Why Peter was at Hagrid's

[pippin_999]

No: HPFGUIDX 39931

I said:
> > >There's no way out of the Shack except through the Willow. 
Of course not, it's a prison for a werewolf. To quote Princess 
Leia,"They don't build them with multiple exits, you know." <g> 
Those windows are blocked by more than boards. Otherwise 
Fred andGeorge would have gotten in. The Marauders must 
have let Lupin out through the Tunnel.

Marina:
> But they couldn't have -- that would've put them all back on 
> Hogwarts grounds, not in Hogsmeade, and Lupin specifially 
says they ran around Hogsmeade.  <<<

He says "Soon we were leaving the Shrieking Shack and 
roaming the school grounds and the village by night."  --PoA 18. 

The Willow cannot be visible from any of the dormitories, or it 
couldn't have been kept secret that Lupin went there. It isn't that 
far from the willow to the Forest, which is probably where they 
spent the bulk of their time. 

Dumbledore: "The forest *on the grounds* is forbidden to all 
pupils" SS/PS ch. 7 (emphasis mine)

 Centaurs are very good at minding their own business.  No one 
else is likely to be roaming the grounds or the village on a night 
of the full moon.  Most sensible wizards are probably indoors 
with the windows shuttered and bolted, especially if there are 
rumors of werewolf sightings.

  Filch is a Squib whose office is windowless and whose duties 
usually keep him inside the school--he certainly wouldn't be 
taking  students for a Forbidden Forest detention on a full 
moon. (Something first year Draco should have thought of.)   

The Hogwarts Gates must be powerfully charmed, but between 
James, who was trusted as Head Boy, and Pettigrew, who had 
the run of the castle as a rat, I doubt that any passwords were 
safe from them. That's probably how they got off the grounds and 
into the village--or they could have even swum across the lake, 
with their bodies hidden by the water and the Invisibility Cloak 
over their heads. It'd be difficult with a werewolf in tow, but it 
seems Lupin was fairly docile with them as long as no humans 
were in the vicinity.

Sirius and James did have some run-ins with Hagrid, from what 
he says in the Three Broomsticks. I don't suppose he would 
have let them off  if he had caught them outright, but I wouldn't 
put it past him to look the other way sometimes. A werewolf's an 
interestin' creature.

Pippin