Some of the scenes are made all the more vivid because we readers know what has happened since 1867. The description of Père Lachaise cemetery for some reason omits the graves of Oscar Wilde and Jim Morrison. The party encounters the Russian Emperor at Yalta, in the very hall that would be used for the famous conference of 1945. Many of the ethnically mixed communities they visit in the Eastern Mediterranean became very unmixed over the next century.
The story kicks into epic gear when the group gets to the Holy Land, the ultimate goal of the journey. I was particularly interested in this to compare with my great-grandfather's account of a similar pilgrimage from nine years earlier. Their stories basically agree, though Mark Twain is robustly cynical while John Joseph Whyte is a devout Catholic; except in one respect - Whyte frequently comments on how fertile the land is; Mark Twain finishes the section with a memorable description of its barrenness. Had the climate changed in the meantime? Or was the American fitting the facts to the story he wanted to tell?
There were a fair number of travel narratives around by 1867 - it was perhaps a more familiar genre then than it was now - but I suspect this is one of the few still read today, as a humorous and contemporary account of Americans dealing with other cultures. Not completely convinced that it merits the attention it gets, though.