The Dome of the Rock is right beside Al-Aqsa mosque in Jerusalem, Israel.
Is it considered a sacred place in Christianity? If so, in what way?
In addition to it's location as the site of the original Temple, and the place where Abraham almost sacrificed Isaac, the Dome of the Rock does still play in Christianity today.
First of all, the Crusaders thought it was Solomon's Temple, so they let it stand.
More importantly today, however, many evangelicals see the Dome of the Rock in End Times prophecy. Many dispensationalists believe that in order for Jesus to return, the Temple must be rebuilt. Because the Dome of the Rock is where the Temple was, many Evangelicals believe that the Dome of the Rock must be destroyed in order to usher in the End of Days. (No, no Mehdi here, we don't believe it should be destroyed, just that it will.)
This particular understanding has led to many attacks on the Dome of the Rock over the years, leading psychologists to coin an ideas called Jerusalem Syndrome in which self-appointed Messiahs will sometimes take it upon themselves to be this agent of the End Times coming.
Christianity,of course, has its roots in Judaism, and as the site of the original Jewish Temple, it would have historical significance, as well as being recognized as a Holy site, reserved for Israel, God's chosen people.
Also, according to some of the end-time scenarios, the Antichrist will make some deal that will allow the temple to be rebuilt, and this will mark the beginning of the Great Tribulation.
The Dome on the Rock itself is not significant to Christianity or Judaism, other than that it's a shrine to another god, from another religion, that exists on the property where the temple should be.
I'd say that the site itself is important but the Dome of Rock is not. This site is believed to be the place where Abraham prepared to sacrifice his son Isaac. But this is only a Jewish tradition and hence not all Christians would agree with its importance.
The Dome contains the following inscription (also from Wikipedia) -
This of course would not be well received by most Christians. So I don't think that the Dome is important to Christianity.