I believe it is open week days until 4pm... There are summit tour buses that will take you up in the evenings to watch the sunset- but they cost $150 per person I think. Car rental companies absolutely forbid you to take their cars up there. (Doesnt stop some idiots from trying, tho...last week on the way up we passed a rental jeep that had gone over the side and rolled over!)

If you get to the summit, there is a hall with info and a video presentation on keck... there is also a viewing room you can step into to see the K1 telescope. To see the more of the facility and the scopes you need to be escorted by an employee and sign a waiver...

Also, if you are not accustomed to high altitude, be careful... it really takes a lot out of you and clouds your brain... in many ways... sometimes I find myself unable to do simple calculations up there- You have to double and triple check everything you do- It really is that bad...

I have only come close to passing out once- I climbed the outside ladder to the top of the K1 dome- but the view was worth it!

The observatory isn't as open to the public as most of us would like, but we do have a legitimate reason to fear vandals- some people have threatened the observatories...

Each Keck primary is made of 36 hexagonal segments 1.8 meters corner to corner- they each cost ~1 million dollars and would take many months if not years to make new ones...and we have only a few spares- someone throwing a handful of change on the primary could do unimaginable damage! So, sadly, we do have to take certain security precautions...

Here is the url to a picture of the primary...

http://groups.msn.com/Laserguidestar/maunakeapics.msnw?action=ShowPhoto&PhotoID=17