MAGUS - Itsy, bitsy spider

The adventurers returned in force to cross the giant chasm. They quickly figured out that the white string was spider's web. First to risk the crossing was Shamil. He doffed his armor and used psionics to lighten his body weight. Let's say he discovered the spider really quickly. Or, rather, the spider discovered him. All the stealth in the world is useless if you are walking around with a shining lamp above your head.

Everybody else just saw Shamil run full tilt towards them on the main line of the web, and getting impaled on a great chitinous limb. The spider then retreated with the unconscious body.

The adventurers reeled[1] but recovered quickly. Daramin flew out[2] surrounded by levitating lamps and, staying at a safe altitude, saw the spider at the center of the web, neatly enveloping the assassin in a cocoon of web. Daramin teleported Shamil back to his magic anchor[3], then flew back at full speed - his telekinesis was running out. He helped himself a bit using gusts of wind, propelling himself right into the cave wall next to the tunnel exit. One twisted arm. Cahir tried to put it back, twisting it the other way. Daramin was out screaming for a while after that. 

In the meantime, the rest of the party inspected the cocoon. Biznard ripped the spider web apart, discovering the unconscious and unresponsive Shamil under a layer of greenish ooze. Dalibor, somewhat familiar with poisons, established that the assassin is under the effects of spider venom. It could be days before he comes to. Luckily, Ylimor gathered his divine powers and slowly neutralized the poison.

And now came the quality content part of the session: about an hour and a half of planning. To their credit, the adventurers scouted the roughly spherical space from all directions, establishing their escape route. They also explored a lot, and I mean a lot, of avenues of action, including torching the web.

In the end, the party first descended to the bottom of the sphere, while Shamil's firestorm elemental distracted the spider. Everybody got down safely using ropes and stuff, except Dalibor who failed a 94% chance of success roll and landed on his face. Shamil then climbed up to the exit[4] and Daramin flew up as well, hammering in some pitons to hold the ropes. Then, miraculously, everybody got up the ropes. Literally all the rolls were successes. Just as the final adventurer tumbled into the tunnel, the spider came crashing in as well, stopped only by the tight space it couldn't get into. With an angry hiss, the monster retreated, and the adventurers (and players) cheered at a job well done.

[1] Eldritch horror-type effect, as they put it.

[2] Technically lifted himself using telekinesis.

[3] An amulet being held aloft by Cahir, resulting in the cocoon appearing in the air, and thudding to the ground.

[4] A tunnel opening similar to their entrance, and at the same height - roughly the center line of the sphere.