The party doesn't know it, but there's an Archmage (the big bad of the campaign) experimenting with wish scrolls, trying to bring his younger self into the future so he can merge his consciousness into his younger body and take over the city of Waterdeep.

The side effect of this experimentation has been chronomagic portals opening around the Sword Coast at random, and last night's was in a reptile cave in the Lizard Marshes near Daggerford. The Blue Feather lizardmen of the area became fanaticized by it and were worshiping the portal as a god, because on the other side of the portal was the inventor of chronomagic, a Netherese archmage who found the whole affair amusing.

The party infiltrated the cave, killed everything, and had a conversation with the Netherese mage before he closed the portal from the other side. The mage was able to give them some information on their eventual foe based on the nature of the portal.

It was fun. Some good combat and campaign exposition. What's extra fun is that the big bad surreptitiously used them to gather the scrolls in (in the form of fragments) in a previous campaign, but none of them really investigated that angle, so he's been gathering his power right under their noses.