Let me tell you what I did in a short session last night.
1. PCs decide to travel from Bratanis Village through the Ghinarian Hills to the Temple-Tomb of Belaras. Route takes them past the dungeons beneath Sky God Idol, where they have adventured before.
2. On the road I decide to roll an encounter - I roll & get an Elf Ranger Maegladher and his giant rat Galadan. Checking my notes, I decide he is a scout for King Kambdum Domnavrente of Diancecht, sent to investigate rumours of war in the north. I can see he therefore was trained at the Grove of the Rising Sun, I know the name of the priestess who initiated him, his Ranger captain et al.
3. PCs exchange pleasantries with the Elf (well, the Half-Orc threatens to eat his rat), he warns them Yusan's bandits have returned to the Sky God Idol dungeons, and PCs continue on west.
4. At the dungeon, the PCs see muddy tracks going in and decide to follow them, but are distracted by an old library (pre-keyed) where the Eldritch Knight is delighted to find a spell book, the Septimus Severian (pre-placed).
5. While PCs are nabbing the book I make my first dungeon wandering monster roll, get '6' -
encounter, roll - Dwarves - checking notes I see these are Bolfi's men, who the PCs fought alongside before against goblins. But these dwarves want money for 'their' books.
6. Failed PC Intimidate checks, a fight breaks out. The dwarves are wounded, one felled, the other asks for quarter and the PCs let him drag away his injured friend. The PCs are worried more dwarves will come, and decide to leave the dungeon.
7. Heading west again, the first (& only) non-rolled encounter of the evening. I decide that Yusan's Bandits raided (sneaked into) a pilgrim group camp last night and kidnapped Lady Lucretia Alamsor of Rallu, a pre-existing NPC with a record of being kidnapped... The PCs encounter Lucretia's assistant Brionny Fortin out looking for her, accompanied by two hammer-armed men who look like blacksmiths. Brionny has previously been encountered but by other PCs, the men are the Alces brothers from Selatine, lent by Lady Vex of Selatine (very long term NPC) to Lady Lucretia to guard her on her pilgrimage. The groups talk, and the PCs agree to help Brionny recover her missing mistress, telling Brionny they suspect Lucretia is being held in the Skygod Idol dungeon.
And we end there.
So, a mix of random rolls, preset locales, pre-existing and new NPCs, etc. Lucretia & Brionny were last seen (by other PCs) on their Ralluan merchant ship docked at Selatine, a couple weeks ago in-game. When I was looking for an encounter, it made sense to me that Lucretia would want to go on the famous pilgrimage to the Temple of Belaras. I knew she didn't trust her own men after an encounter with pirates on the way north, and so seemed likely she would take guards from Lady Vex at Selatine - but Vex is only just starting to rebuild the village (after overthrowing her brother Hytirus, who had been enspelled by an evil priest of Thanatos) and she wouldn't likely spare either of her two real warriors, Epicaste & Vuthrik. Hence the Alces brothers, the Alces family being loyal to Lady Vex.
The actual session log (blog NSFW):
Rob Conley's blog post from the same rpgsite thread - http://batintheattic.blogspot.co.uk/2017/08/my-axioms-of-sandbox-campaigns.html