This is an active noble house with a bunch of odd nooks and crannies from generations of adventuring and family wizards. The entries below are all the mobile encounters that could happen, expanding on the entries above:
2. Stray monster from the Hollow Hill - the caverns which the original fortress was built on were never cleared. Normally the underground beasts avoid the still, empty sections but noise and light can draw them up - particularly if there have been other combat encounters recently and carrion is lying around. Carrion crawlers, phase spiders, giant centipedes, otyughs or other underground predators can turn up.
3. Family up to adventure - you find a group of the youngest cousins of the house dealing with some heritage wierdness. Some well equipped, in heirloom arms and armour, others along for the fun in walking gear and picnic baskets, they will treat you as a wandering monster they have run into unless you convince them to just arrest you for trespass. This will be loud.
4. Wizards arriving / departing - whether flashily (in the courtyards) or subtly (inside) one of the wizard relatives appears. They are not familiar with the palace occupants and are here on their own business. Their attitude is 'neutral, in a hurry'. Roll d12+6 for the wizards level if relevant.
5. Dangerous critters. Oozes, large insects, minor undead from disturbed tombs or mimics are often found in the lower parts of the keep. They will be hungry and aggressive.
6. Palace repair team. A small group of surveyors and masons can be found clustered in a camp in one of the old great hall fireplaces. Fully dark-adapted, they tend to stay down here for days to reset traps and alarms, close doors and set barricades to keep the worst critters and monsters from the main part of the fortress. Happy to share their fire with other common folk, will scatter up chimneys and through servants passages if facing aggression and raise the alarm.
7. Wyvern messenger arriving - one of the duchy's mounted rangers - either landing their beast (outdoors) or with other members of the household searching the palace for whatever they are here to fetch. Indoors they are typically searching the walls and bookshelves for particular old trophies, treaties or magic items that have been requested elsewhere.
8. Aggressive vermin - stirges, trash gryphons, rats or other swarms of beasts that live in the walls or sneak in from outside.
9. Children sneaking and spying - children of the household creeping about watching the goings on of the household. If approached correctly (bribed with sweets) they can answer most questions about where things and people are and how to get there.
10. Senior guards w/ prisoners - armed and armored palace guards moving prisoners - either hauling intruders to the dungeon or moving prisoners to/from interrogation. Will challenge any intruders they spot but are distracted by their duties.
11. Honoured guests - a group of high ranking guests installed in these spruced up rooms. Servants are waiting on them and a minor member of the family is entertaining them. People are distracted, the atmosphere is festive and food and drink is flowing freely. Eavesdropping will pick up on local intrigues. People are not alert.
12. Guardsmen on watch - lightly armed and armoured guards on watch. Bored, they will probably (4 in 6) challenge any passers by and raise the alarm and attempt to hold anyone that cannot explain why they are wandering around. Guard locations are usually along corridors, stairwells with good sight-lines. Legitimate business will get brought to the Guard Captain, they will engage any obvious threats (e.g. pursuing monsters) or try to rescue people in danger.
13. Servants dashing about - carrying food, laundry or furniture, this party of servants is going to politely but firmly jam this location up while they are passing, acting on urgent instructions from higher up. They will ignore anyone who does not block them.
14. Family arriving, departing - a fuss of senior members of the family trailing servants, clerks and guards on their way to or back from somewhere. Snippets of daily business can be caught if you eavesdrop or this can be a chance to speak to someone in charge. Threats to the family will bring fast, lethal response.
15. Servants about daily business - cleaning, fetching and carrying, these servants are gossiping and lurking about listening or striking up a conversation will pick up the current goings on in the keep. Threatening or scaring the servants will raise the alarm.
16. Guild officials here for meetings - either meeting in the public offices, attending planning sessions with the clerks or viewing part of the palace ahead of complex repairs. Can comment on local news and politics.
17. Temple clerics here to meet family - members of one of the city temples here to discuss matters in the city, meet privately for matters of conscience or maintain some of the numerous small chapels and tombs within the palace. Can offer views on any matters religious.
18. Local nobles here for social call - being hosted by the family touring parts of the palace. A masterclass in social put-downs and cutting words is on display. People are distracted. Trailing along can pick up information about the palace and its history.
19. Clerks at work - either at desks in their offices or cataloging the newly re-opened parts of the palace, they will have a trolley with scrolls and numerous junior clerks. This location will be a mess with everything laid out for inspection, they will be upset if people try to disturb everything.
20. Cleaning crew - servants with mops, buckets, scrapers and shovels to deal with the aftermath of some vermin or critters. 50/50 to be on their way back, tired, filthy and hauling buckets of gruesome innards.
21. Guards dealing w/ hazard - armed and armored palace guards on their way to deal with something the servants spotted. 1-2 on d6 they are hurrying on their way, 3-4 they are on their way back, dirty and splattered with gore, 5-6 it was a tough fight and they have ditched their shields and are hauling some of their number injured.
22. Prisoner transfer to the border forts - either in the dungeons or the courtyards a penal-column of prisoners is being assembled or marched out for the border forts. Guard presence is heavy, with crossbowmen and adepts standing off. The guard captain is here and alertness is high for break out attempts. Strangers will be challenged sharply, nerves are on edge.
23. The Duke - you stumble upon the Duke and his entourage up to something in the palace. Probably companions are a half dozen advisors, his court wizard or other senior members of the family. The Duke is a gruff and grizzled old survivor who fought off a murder cult in his youth. Twitchy about assassins and will react badly to those who sneak and hide. Approached openly he will question his guests about their business and direct them to whomever of the household needs to deal with it if it seems a legitimate reason to be present. Persuasive interlopers may get themselves a commission to go deal with the problem and report back. Bad explanations get passed to the Guard Captain for interrogation, really irritating interlopers will get tossed in an oubliette.
24. Magical space - you access one of the extra-dimensional spaces built in over the centuries - either the old elf-queens wardrobe that leads to the Feywild, one of the non-euclidean passages built by a wizarding cousin or a magical painting.
To test all this we take cousin Lara, competent swashbuckler who cannot sit still with 24 hours to kill who decides to wander about the Palace. Every hour she picks between going deeper into the Palace (1-2 on d6), staying on this level (3-4) or heading back to the core areas (5-6). I rolled up a bunch d6's to get her random path through the palace then rolled the relevant encounter dice sets depending on where she was every hour.
|1||6d4||5||16||Guild officials here for meetings|
|2||6d4||5||13||Servants dashing about|
|3||6d4||1||14||Family arriving, departing|
|4||4d6||1||12||Guardsmen on watch|
|5||3d8||2||22||Prisoner transfer to the border forts|
|6||3d8||4||9||Children sneaking and spying|
|7||4d6||6||14||Family arriving, departing|
|8||3d8||2||7||Wyvern messenger arriving|
|9||2d12||2||17||Temple clerics here to meet family|
|10||3d8||5||7||Wyvern messenger arriving|
|11||3d8||3||16||Guild officials here for meetings|
|12||2d12||2||12||Guardsmen on watch|
|13||2d12||4||17||Temple clerics here to meet family|
|14||2d12||4||9||Children sneaking and spying|
|16||d4,d20||4||10||Senior guards w/ prisoners|
|18||3d8||6||13||Servants dashing about|
|19||2d12||1||6||Palace repair team|
|20||3d8||6||13||Servants dashing about|
|21||2d12||1||19||Clerks at work|
|22||d4,d20||1||6||Palace repair team|
Does what I wanted it to do - 6d4 and 4d6 trended to mean quite a bit, 3d8 and up got swingy and the weirder things started coming out but we still got some of the more standard things. I like this for the effect of stirring more strangeness in on top of the relatively mundane - especially for places where some parts of a site are inhabited and active and those people could be found across the whole site.
The updated tabulated numbers look like this, thanks to our mysterious stranger who worked it up on AnyDice for me: