Disclaimer: Don't own them. Wish I did.
Author's Note: I'm using the British way of numbering floors. Ground floor, then 1st floor, etc.
Harry met up with Prof. McGonagall a the main entrance to the castle with his broom as required. McGonagall wore trousers instead of her usual long skirts. Her broom was of an unknown make not a racing broom at all. "Excellent you are on time. I'm going to cast a warming charm on you Mr. Potter. It is truly cold out there. The sky is clear and there is a wind from the North." McGonagall said. She cast the spell and Harry instantly felt toasty warm.
"Why don't we learn this Warming Charm?" Harry asked as they went outside.
"It's a NEWT level charm. If you take a charms NEWT which I do recommend you'll learn it your 6th year." She4 said as the exited the castle. "Do you see the wards Mr. Potter." she turned to face the door.
Harry turned to face the door himself. "Faintly by the door. It looks like those shields that interlock. You know the ones the Romans used. The blue and red shields aren't quick locking together." Harry described what he saw.
"Good. Now mount up. The Gryffindor wards cover the outside of the castle from the ground floor up to the 5th floor. The outer wall wards are different and are dealt with by rituals done by the four heads of house and the Headmaster and don't concern us. Now I want you to find where the wards are weakest." McGonagall ordered.
Harry studied the wards for a moment the color of the wards where stronger to the left while to the right the colors faded in and out. "I think the wards grow weaker to the right. The colors are faded and sometimes fade out altogether." Harry told her.
"Correct. Now you may run into wards that don't run true to that pattern. Wards of concealment and the like tend to fade as they get stronger. Other wards do other things. Prof. Flitwick will teach you more about them during your mage sight lessons." Prof. McGonagall said as she rose to the third floor. "Mr. Potter if you will go ahead of me please and below me."
As the followed the castle exterior Harry noticed small knots instead of the large knots he found with the Slytherin and Hufflepuff wards. Most covered windows which he knew could be opened to let in breezes. Several covered spots where it was just stone wall. After the third such spot Harry asked. "Professor why are there knots there it's just stone?"
"Physical changes to the castle over the centuries. Those spots used to be windows. We are coming to the one spot the students don't know about the last physical change to the exterior of the castle. It's a tower over the lake called the Fairy tower. It's been sealed off since it's last occupant retired in 1934. It was meant to house the Heads of House."
"Could Brown's Master be living there if it's sealed off." Harry asked.
"Only if he was insane. The rooms can change at a thought and if you don't have the utmost control over your thoughts the rooms can run amok. My one encounter with the Gryffindor set of rooms had me wishing for tea and getting a hedgehog." McGonagall said.
As they came up on the tower Harry blinked. It floated over the lake with it's only attachment to the castle a narrow bridge at the midpoint. Here the wards glowed strongly each proper with no twists or malformations that the other wards had. The complexity of the wards baffle him. While some of the wards do fade out they do so cleanly. As the tower can't be seen from the lake or any place else on the grounds Harry expects these are the wards concealing the tower from view.
"I'm not seeing any thing wrong with the wards. But I could be missing a lot. They are so complex I don't know were one begins and another one ends." Harry told Prof. McGonagall.
"You and me both. None of the current staff have been able to untangle them. It's an on going puzzle for the staff. However since the wards of protection are the standard for Hogwarts and they look to be in good shape we can bypass the need to examine them further." The clock tower rang 11 PM. "Bedtime for you Mr. Potter. When you return to Gryffindor I want you to write up what you have seen on tonight's inspection." She told him as they finished up above the main entrance.
Instead of landing there Prof. McGongall had his follow her towards the Gryffindor tower to just under the eaves. There she said a word and a section of the wall peeled back like that in Diagon alley. She flew inside and landed. Once she did torches lit up a small room with empty broom racks similar to the ones in the changing rooms at the pitch.
"I'm quite sure you have found the guard barracks scattered around the castle by now. This is another of the old defenses. There is one in each of the original towers when the castle was built. I've placed special wards up here to seal it off from the students. Your are not to come up here understood." Prof. McGonagall admonished.
"It's like the two other kitchens in Hufflepuff territory." Harry clarified he understood.
"That will do Mr. Potter." Prof. McGonagall said as she opened the door to room then stopped Harry before he exited to flick his wand at him. "We will exit this room in the Girl's dormitories I have temporarily neutralized the protections that restrict boys from this area. Once in the common room the spell will be canceled."
They went down the stairs into a linen closet then out into the stairwell for the girls Dormitories. In the common room the 7th and 6th years are waiting. Montgomery handed McGonagall a slip of parchment which she read. "You are with me Mr. Montgomery since you still are underage even with your parents permission."
Harry tuned them out as he went to the table he had set up prior to the inspection of the Gryffindor wards. He drew his map marked were the hot spots where. Then made a notation for were the Fairy Tower was. By that time the common room had cleared out save the lone fifth year prefect waiting to see that Harry heads to bed. Since he is finished he does so. Ron is waiting up for him.
"Anything interesting?" Ron asked.
"Tell you before breakfast." Harry told him as he changed into his pajamas.
"Good I've got the perfect spot for the trap." Ron said. "Hermione says that she's got some progress on the transportation spell for us to."
"Finally. Remind me to write Remus about the map some time this week would you." Harry commented as he climbed into bed. The candles dimmed then went out. Only the one by the door stayed lit.
The before breakfast meeting took place in the nearest of the barracks rooms to the tower. "Hermione does Hogwarts a History mention anything at all about the Fairy Tower. Prof. McGonagall said it was the last physical change to the castle." Harry asked.
"In the Unbridged self updating version it does. That one is in the restricted section though. What I know from my quick looks through it isn't much. The Fairy tower was added to the Castle in 1853 at the request of the then head of Slytherin Calanthe Ravens, she taught DADA for 125 years retiring in 1934. The longest living teacher on record." Hermione told them.
"Would it tell you the spells used on the tower by chance?" Harry asked.
"I'll have to go back and check some times it does, some time it doesn't. I'll need to borrow your cloak to do it. My pass ran out on the 31st."
Ron looked up from his study of the map. "Any other surprises last night?" he asked.
"Just a few blank spots on the wall were Prof. McGonagall said that at one time there had been windows. Here , here and here." Harry pointed them out. "Then the empty Broom closets on the top of each of the original towers."
"I know why this area is blank. The room was converted to a test area for the Curse Breakers club in the 18 hundreds. It's currently used as a dark room for the Photography club." Hermione told them.
"I think I'll set the twins to finding out what the other two rooms where changed for. Now I found the perfect spot for the trap to get Brown." Ron began as he got out his map of the castle. One of the advantages of using these barracks rooms was that they could leave things here with out some one else getting a hold of them. "This corridor is one he likes to use after lunches. Christine Applegate has volunteered to be the bait. She's a third year Hufflepuff with the begins of the Healer's gift. She's also the daughter of two muggleborns. For our purposes this passageway has two advantages. A point to point corridor and a concealed room here. A couple of witnesses at each of these points under some form of concealing spell from each house." Ron trailed off.
"You've asked about this with the teachers?" Hermione asked.
"Not yet. I've an appointment with Prof. Sprout tomorrow to get Christine's permission to be bait. With out that we have to wait." Ron said.
"Okay, last thing then. There are five possible spells we can use as transportation. I need to talk to Prof. Flitwick about the theory behind them before I narrow it down to the three Prof. Snape wants. There is a sixth one I'm going to adapt a bit. Frankly I think it's going to be illegal anyway. It's going to be a last ditch get the hell out of there sort of spell."
"Hermione those type of spells are always illegal." sighed Ron. "Please Breakfast."
"Let's go." Hermione said
Everything they had taken out is put away and locking wards unique to the three of them lock their individual chests.