I looked at the schedules for routes 560, 564, 565 and found that although there are 4 buses per hour, they are not spaced for 15 minute headways. The 560 departs Renton at :05 and :35 and the 564 & 565 combined depart at :02 and :32.

A barrel-shaped, but stationary, restaurant on Fernsehturm Stuttgart, a TV tower in Stuttgart, Germany, built in 1956, was noted as the inspiration for the idea of a revolving restaurant. A revolving restaurant on Forianturm, a TV tower in Dortmund, Germany, was brought into service in 1959. John Graham, a Seattle architect and early shopping mall pioneer, is said to be the first in the United States to design this sort of restaurant when he created La Ronde on top of an office building at the Ala Moana Shopping Center in Honolulu in 1961. Graham later also used the technology to build the revolving restaurant still in service at the top of Seattle’s Space Needle.

So, not so historic but still cool.

Show Routes 560, 564, 565 between Bellevue and Renton which has four-plus buses per hour on weekdays, although it does not meet your criteria on weekends.

Show Routes 510 and 511 between downtown Seattle and Jackson Park on I-5. Depending on what the Board decided today on the amended 2009 Service Implementation Plan (what’s the news on that STB?), there could be a significant increase in service in September. Even today, there are three buses an hour between downtown Seattle on Jackson Park on Sundays (making the park-and-ride at NE 145th Street my choice for attending a Mariner game).

How many revolving restaurants are there?

There’s been enough buildings that have copied the space needle to show that it has had some world-wide impact.

Name three. Two? I’ll agree the Space Needle is something worth preserving but Worlds Fair attractions like the Awful Tower had a lot of local support for being torn down. They’re now tourist attractions which have created history so that won’t happen. FWIW I think the Space Needle is sort of cool and in touch with Seattle’s image of a modern city. I’d have been among the majority of Paris residents that wanted the Eifel tower torn down. We have pictures.

Again, my point is that a building can have historical significance as a structure, and a building can have significance as a place where history was made. Those are different things. And the oldness of a building isn’t always the point. Events in Philadelphia Hall changed the world more than events in a random roman building in North Africa, etc.

I think I’ve made my point.

Grade I: buildings of outstanding architectural or historic interest.
Grade II*: particularly significant buildings of more than local interest.
Grade II: buildings of special architectural or historic interest.

Wikipedia contains more info on the topic of historic landmarking.

Whatever cave Osama Bin Laden planned the WTC attack has had history take place in it. Again, not an important place.

Maybe, but if you could identify Jesus tome that would certainly be historic, important and landmark.

Bell Labs, don’t know. If it were a museum it might be cool. I’m guessing it’s been bulldozed. No great lose because the inventions live on. If you’re in Spokane Valley they have a cool local museum with a working telephone switch system. I’d hope they keep the model T assembly building but we have preserved umpteen thousand model T’s so that’s OK.

Space Needle, important to Seattle but the world? Not so much. I’d put it above the hat and boot in George Town but personally, not so much. But then I think the Eifel tower is an ugly radio antenna that’s more hysterically significant than historical. Obviously I’m in the minority on that one.

You can say that more historical important events took place inside of Parliament and the Tower of London, but under that definition both of those are less historical than whatever tent Alexander the Great slept in outside of Chaeronea and whatever factory building the Model T assembly line was in. Even then, that’s still a handful of buildings.

Well, if you had Alexander’s tent it would be damn significant. The factory building the Model T assembly line was in is still there in Detroit and I sure as hell hope it can be saved. That I would agree has historical significance but it ain’t Westminster, Saint James, Parliament,… You seem to be forgetting what an influence the church was on civilization.

Bell Labs are unimpressive (and unimportant) buildings that had world-changing events take place inside of them. They aren’t landmarks of any sort. Whatever cave Osama Bin Laden planned the WTC attack has had history take place in it. Again, not an important place.

Space Needle: Landmark? Yes. Historical? Not really.

Smith Tower: Landmark? Yes. Historical? Yes.

That’s how it works. It doesn’t matter whether anything “historical” ever takes place under or in the Eifel Tower. It’s a historical landmark.

By your definition Palace of Versailles would be the most important building of the 20th century.

News to me, the Palace of Versailles is a 20th century building?

Or really what “landmark” means at all…

There are so many important world events that happened in completely unimportant buildings, and even some that happened in new buildings. By your definition Palace of Versailles would be the most important building of the 20th century.

Look at Shanghai, Hong Kong, Bellevue, Seattle, etc. etc. Which building had more of an effect? Tower of London or the Empire State Building?