That's a Daddy Longlegs. Or a Cellar Spider. This one is a Marbled Cellar Spider, native of the Mediterranean but we have cellar spiders over here. They sit in their messy webs behind the toilet all year, slowly getting bigger and bigger but not causing any harm. Then some evil bastard sucks them up the Dyson. They don't deserve it, they're clever. There's a small one in the shower here, or rather in the corner of the ceiling above the shower, 8 feet up. I've just taken a shower and just after I'd turned the water off but was still in the cubicle, I saw the spider abseil all the way to the bottom, dodging the soap dish on the way and land on the top edge of the shower tray. It took him/her about 10 seconds. It didn't move and I thought it was stuck in the water. I watched it for a few seconds and it didn't move. I got out and started to dry myself and as I did so, the spider moved and hauled itself back up to the ceiling in about 20 seconds.
The whole operation took about 2 minutes but then it occurred that this was actually quite an astounding display of animal intelligence. This tiny organism, with a brain a few microns across, had worked out the best time to get a drink in a hostile atmosphere. It knew that when someone goes in the shower there's water about but that it's dangerous to drop down when the shower's on, so it waits until it's off. Then it drops, far enough away from the walls not to get stuck on the wet tiles, picks the top of the tray where there's no pooling, has a drink and then goes home. Maybe I'm easily amazed but I think that's incredible.