For the weary, determined tourist to Greece, Italy, Spain, Bulgaria and environs, wall-eyed after a surfeit of Byzantine churches, Mr. Lancaster's cheerily biased, pleasantly, instructive tour will be a happy restorative. In an introductory ""perspective,"" he tiptoes lightly along the high tides and muddy backwaters of cultural invasions, retrenchments, and the religious schisms and coordinations which characterized the Byzantine Empire. There is a brief discussion of the nature and origin of the True Dome, and Lancaster casts his two drachmas for a derivation from ""a large Hellenistic center of civilization."" Then on to a variety of sites with witty prejudices and charmingly communicated gratifications. He has no patience with sentimental elaborations, the massive and unimaginative (the Tomb of Theodoric in Ravenna is ""an unattractive mausoleum. . . a corner of a foreign field that is forever Deutschland"") and he contemplates some reclamation projects with a heavy heart: ""It is far better for the House of God to fall into the hands of the Infidel than into the hands of the Office of Works."" There are a few practical tips on church visiting (he warns of one verger who ""stinks to high heaven and is a mine of misinformation""). Of greatest value to the tourist, however, are the in situ appreciations. With drawings by the author, charming but not too explicit, this is a useful, casual guide, easy (in its compact format) to tote.