Between Flayer and Flail

Following the commoners, the party find them attacked by two flail snails.

After a brief battle the snails are defeated but their death cries carry throughout the corridors and draw a gelatinous cube.  Then something strange occurs.  Behind Zaven appears a door and stairs that lead to down to a landing and a bare stone wall.  The party pile into the "new" corridor and close the door behind them.
     After resting 4 hours, the group is discovered by the small humanoids that shot up Zaven and Dusty before.

The creature's bite and club attacks almost overwhelmed the group but they were finally defeated. The party managed to get another 5 hours of rest and rememorize spells as well.
Which way will they explore next time?