The 5-Room Dungeon is the most reliable adventure design framework in tabletop RPGs.
The 5 Rooms
Room 1: Entrance/Guardian - A challenge that gates entry. Room 2: Puzzle/Roleplay - Shift the pace. Make players think differently. Room 3: Trick or Setback - Something goes wrong. Room 4: Climax - The big fight or major decision. Room 5: Reward/Revelation - Treasure, plot twist, or both.
Worked Example: The Thornwall Crossing
Room 1: Goblin checkpoint with a captured merchant Room 2: Collapsed bridge puzzle Room 3: The bridge was a trap - goblins alerted their boss Room 4: Hobgoblin war chief in a multi-level cavern fight Room 5: The merchant's cargo reveals a map to something bigger
Use the Encounter Kit to generate balanced encounters for each room.