Deep in a wooded valley of the Rila massif, behind walls that look built for a siege, a courtyard opens in black-and-white stripes under three tiers of wooden arcades. This is Bulgaria's spiritual centre: it carried the language and alphabet through five Ottoman centuries, and its church is covered in twelve hundred frescoes. Only Hrelyo's Tower, square and grim, survives from the medieval foundation — everything else was rebuilt in the nineteenth century.