d100 Dungeon Seals to Trap Heroes

So if your players raid a dungeon and run after a few encounters cos the wizard ran out of spells. Nobody hurt but it slows game down and is a bit less heroic to flee from a scratch. Heroes suffer, hunter or alley cut throats execute with little personal risk. No risk is not adventure it is shooting fish in a barrel. One option is every time party returns the guards increase and every encounter is more ready and monsters hide loot more or sent women and children and loot to the boss monsters brothers dungeon.

A simpler approach - seal them in and force them to survive without pit stops. they will moan but will have a much more exiting adventure.

Some of these might requirethe threat to be demonstrated possibly from a dead and plundered party.

d10
1 Disaster - mud, avalanche, snow, quake
2 Organic Barrier - slime, fungi, mould, plants
3 Deathtrap Barrier - entry is a huge trap
4 External Siege - enemies establish siege
5 Siege Defences - residents fortify front to keep out invaders
6  Monster Barrier - terrible monsters have settled in entry
7 Cursed Seal - evil magic such as undead or demons or harmful effect
8 Magical Seal - a magical barrier like force wall, fire wall, elementals
9 Weird Barrier - something truly strange keeps people away
10 Supernatural Barrier - possibly placed by gods

d100 Dungeon Seals to Trap Heroes

01 Mudslide seals entry

02 Quake collapses entry or causes rockslide
03 Snow or Ice seals entry (posibly magic)
04 Water floods entry way
05 A fire damages tunnel collapsing it
06 Volcanic fissure seals with lave
07 Poison gas flooded
08 Plague corpses scattered around entry passages
09 Accidental explosion from alchemist or wizard
10 Poor materials and maintenance bring down roof from noise
11 A horrid flesh eating lake of coloured slime takes over entry
12 A lake of fleshy protoplasm birthing tiny monsters blocks entry
13 A deadly fungus garden takes hold
14 Killer plants block entry way
15 Plague of huge d4 1=snapping turtles 2=killer frogs 3= snakes 4=lizards
16 Everything overgrown with toxic mould and contagious spores
17 Mobile shambling compost heaps have filled entry for group seasonal fermentation
18 Something horrible has laid thousands of eggs with hyper voracious flesh eating young
19 Crawling with d4 1=rot grubs 2=kyuss maggots 3=fleshbore worms 4=zombie worms
20 A swarm of giant bugs builds a nest d4  1=wasps 2=bees 3=ants 4=termites 
21 Entry way collapse when secret kobold tunnel underneath collapsed
22 Barrels of explosives with kobold suicide pyromaniacs on guard
23 Celing closes sealing entry and crushing
24 Hundreds of poison arrow or dart traps installed
25 Walls extrude spikes and close in on tunnel
26 Entry covered in flammable fuel or tar with kobold ready with a match
27 Weakened beams bringdown roof if stripline tripped
28 Concealed automated bolt throwers (possibly manned)
29 Huge boulder released which eventually blocks entrance
30 Whole corridor drops suddenly sealing entry
31 Bandits build a palisade and shoot anyone leaving
32 Military build trenches and sharpened stakes, with crossbow troops
33 Military seal entry and pump in smoke if detect anything trying to get out
34 Military set up ballista guarded by pikemen 
35 Military cavalry unit on guard charge anything leaving
36 Murder hobo gang build camp in entry and kill anything threat comes close
37 Religious order of templars with paladin hero to kill non good agents l
38 Local knight and his friends camp here to slay anything that comes out
39 Barbarian tribe come to camp so youths can someone to kill for festival
40 A nasty mercenary force come here to contain entry no questions asked
41 Monsters bury entrance under d4 1=rubble 2=dung 3=garbage 4=dirt
42 Open murder hole hatches in ceiling with boiling oil and lead ready
43 Entry thick with monsters with shield walls and pikes
44 Wicker siege sheilds cover archers ready for assault 
45 Covered in poison caltrops with archer guards
46 Kobolds brick up and if hear attempts to get through add more layers and buttresses
47 Monsters pump irritating or nausea inducing gas into entry
48 Monsters seal their end and flood entry with sewerage when intruders enter
49 Monsters stock with deadly fungus and monsters that blocks tunnel
50 Monster cavalry force occupy entry and use as stables for their awful mounts 
51 A dragon moves in to set up a lair and is keen to assert authority
52 A family of giants move in with a big cooking pot, invite visitors to dinner
53 A huge band of ogres move in and set up fortifications for magi clan leader
54 Gigantic burrowing monster semi collapsed entry and now live there
55 Gremlin colony infested in entry, hundreds then a thousand swarm from cracks in walls
56 Trappers, mimics and other camouflaged monsters infest entry
57 Giant paralysing carnivorous jelly blocks entry and is difficult to notice
58 Invisible stalkers have been left here by evil wizards for laugh 
59 A froghemoth has come here to spawn and likes tasty food coming into nest
60 A flock of wyvern's nest here, the two tailed local variety
61 Cursed glyphs inflict evil debilitating magic on any who pass
62 Undead phantoms led by non-corporeal undead arise if intruded
63 Hundreds of spirits swarm here and await bodies to possess
64 Corpses scattered around entry arise as undead that seem endless
65 A small army of wights has come seeking a new lair and will build a tomb
66 Lycanthropes come here socially and area stinks, can infect intruders with taint
67 A travelling Kaiju that travels by night has snuggled in here for a nap, can eat in sleep
68 A rare gathering of many dozens of owlbears hooting incessantly for weeks
69 A dragon couple have crept in here for violent lovemaking for a few weeks
70 A travelling monster freak show released stock here rather than let sherriff kill them
71 Magical walls of fire block passage
72 Magical Ice fills entry, possibly with trapped victims inside
73 Force wall blocks entry
74 Fire elementals guard this spot - a temporary planar node
75 Air elementals guard this spot - a temporary planar node
76 Earth elementals guard this spot - a temporary planar node
77 Water elementals guard this spot - a temporary planar node
78 A magic mirror makes evil clones of any who pass
79 Entry actually sends passers to a different time or plane one way
80 A bubbling pool of chaos here forming shoggoths and worse, guarded by demons 
81 Tunnel filled with millions of  screeching rats swarming into impossible shapes
82 Undead mammoths migrated here from local tar pit, hate two legged freaks
83 Hundreds of goblins orcs and other species fused into a disgusting living lake of flesh
84 Blocked by hundreds of tons of candy, cake and other sweets, giant ants attracted
85 Blocked by fused bones of hundreds of skeletons animated by mad necromancer
86 Modrons have a foothold base, local intruders to be put in stasis boxes for a aeon
87 Silver knights of gith come to test mortals psionics, kill enemies and build a outpost
88 Serpent men came and filled full of explosive runes and magic traps
89 Special force troops scouting from other dimension awaiting extraction 
90 Flooded with blood that acts as unholy water that cancels recently used magic healing
91 A local petty god guards entrance for a short stay
92 Minor elder god has awoken and uses this as lair and flophouse for cult pilgrims
93 A minion of a god has been sent to keep any from passing
94 A portal to hell has opened with devil guards and a burning hellscape
95 A demigod hero camps here challenging all comers, if defeated their parent notices
96 A saint with a travelling shrine, only converts may pass, violence is impossible
97 A fabulous divine beast will only let pass those who accept it's quest or puzzle
98 A angel with burning sword and eyes guards here "I dunno why, nothing personal"
99 A monster god has appeared and monsters from many dungeons come to see
100 A mighty god watches and will block passage, destroying those who dont get hint