P I T S
Don't play around the bottomless pits.
First off, these pits are not bottomless, they just simply kill you when you fall in them. Like the space arena Q3dm17. all you need to do is first off make sure that there are no leaks, (make sure that there are walls all the way around, and a floor). Make a brush that covers the bottom of the pit with more than 64 height (just makes sure that then hit the trigger before the bottom) and give it the common/trigger shader. Right click in the 2D view and choose trigger/trigger_hurt while the brush is still selected. Now push N to bring up the Entity window for key type in dmg and for value type in 9999. Make sure that you have SILENT and NO_PROTECTION is checked. Silent doesn't make a burning noise (like lava) and no protection means that armor cannot help you.
If you want the player to scream when they fall into the pit the make another brush with the common/trigger shader and plce it above right where they fall from and make it about 8 units high and as big as you need for length and with (the whole point is that the player passes through it). Right click in the 2D view and select trigger/trigger_multiple. Push Esc to deselect everything and right click again and select target/target_speaker. Push N then for key type in targetname and for value type in a name like scream. Now make another key that is noise and for value type in *falling1.wav. This will make your player scream before they get gibbed.
It's like this, your player falls through the brush that has the target_speaker attached to it then they scream. Finally they hit the bottom trigger_hurt and explode just like they hit an invisible bottom.