So all those wooden seat-with-a-hole-in-'em-thingies you see over the garderobe holes in historic castles are there for modern sensibilities? The things one learns.
What about getting thrown into the Dungeon, and having the inside contact arrange for a well timed release. Just a set of clothes and some basic u derstanding of the castle and the MC could create havoc!
This could work as long as you didn't need to get into the keep. Most dungeon cells as we think of them today were generally built into gate houses and wall towers rather than the inner sanctum.
Well, maybe you're looking at it from the wrong angle. How about taking one of the well-known ways of sneaking into the castle, but throw a ton of things gone wrong to make it complicated and interesting? For example, he could try sneaking through the front gate, but he gets distracted by a whore hitting on him and almost tells her his name in front of the guards.
I'm not one to make suggestions since I suck at medeival and castle setting stories, lol but maybe you could have him planned out reinforcements to start a conflict battle at the front gates, which would distract guards while he sneeks in or for comedy have women distract the guards at the front gates while that gives him time to infiltrate.
Many castles had a postern gate, which was basically a small, well-defended door that could be opened to let out a scouting party or whatever without having to open the main gate. It required somebody on the inside to open it, but a strategically placed bribe or a person on the inside with a grudge or a thirst for vengeance might be used. In one of her books, Ellis Peters described a castle with a vine that had grown up on a wall. A young boy noticed it and figured that if he was careful, he could climb it without being detected, since much of it was in a "blind" spot directly under the tower. That's how he got into the castle.
I think pepys has gone to the nub of the question - you need to know what sort of castle you're dealing with. Is it a town or city keep? A frontier or trade route control? A fortified house? I always feel that people expect castles to be far bigger than most actually were. People think Carcassone ( I know - modern pastiche) rather than a Peel tower. Even a big one like Krak des Chevaliers is pretty small despite its importance.
You could take a cue from actual history. Persian King Cyrus rerouted a river and snuck under an iron river gate white the Babylonians were celebrating. He took the city in 539 BC without a battle. In your case, you could use a small creek. It could be done in one day without notice on a festival day. Plus, festivals are always fun. At least the renaissance festivals in our areas are.
I'm just gonna throw in my two cents here. Have you researched historic incidents of how enemies have made it into Castles. Obviously as many have mentioned Castles were meant to keep people out and provide defences to siege etc. However i'm sure there were ways that people didn't even think of or where the occupiers of the castle were very set in their ways or had something of their personalities to exploit. In the same way that criminals have been caught in the past as they couldn't do without getting their favourite food from a certain restaurant. It might be a more substantial thing to tie in to the story to have the occupiers downfall is their own making. I always think it adds an extra bit of poetic justice when the antagonist provides their own demise. The protagonist could almost get the antagonist hooked on a certain thing to guarantee that they gain access to the castle, they could cause jealously in them to the point that they let their guard down. This is obviously quite a long game and would depend on the rest of the story but might be a idea.
It's true it has been done a lot in fiction before. I have a few ideas that, while I don't know if they're original, I haven't seen done in stories; * Seduce someone on the inside looking out to covertly let them in (maybe a noblewoman looking out a window - you could even throw in a nod to Rapunzel). * If there's access to magic, how about a teleportation or portal spell. * Creating a distraction that draws people to one side of the castle so he can sneak in another side. * Use a trick to get them to open the gate and sneak in while they're distracted.
Probably late but one way you can go is the MC getting help from the inside. Maybe a thief or merchant (basically anyone that could benefit from the alliance). Over hears the MCs dilemma, offers assistance in exchange that they follow the agreragre. Merchant can help him get in straight threw the gate. So can a member of council or Gaurd. And a thief would probably familiar with the layout and know of better passages.
Have him dress up like a woman and walk in with a male escort since back then, the guards probably would have only addressed the male. Or, create a unique diversion that the guards would have to walk away, or look away while you sneak in.. like some nude people arguing whilst drunk.
Pull a Cyrus the Great. Have another force dig channels to divert water from a moat/entrance so that he can literally walk right into it. If water runs through the castle it can withstand a siege longer. Or, do the same except the castle is surrounded by a walled town and therefore does not have walls of its own. Then if you like you could draw other parallels to the great Empire builders of old and foreshadow a great conquest if you like.
