The great grey bulk of St Giles Cathedral dates largely from the 15th century, but much of it was restored in the 19th century. One of the most interesting corners of the kirk is the Thistle Chapel, built in 1911 for the Knights of the Most Ancient & Most Noble Order of the Thistle. The elaborately carved Gothic-style stalls have canopies topped with the helms and arms of the 16 knights – look out for the bagpipe-playing angel amid the vaulting.
Properly called the High Kirk of Edinburgh (it was only a true cathedral – the seat of a bishop – from 1633 to 1638 and from 1661 to 1689), the church was named after the patron saint of cripples and beggars. The interior lacks grandeur but is rich in history: a Norman-style church was built here in 1126 but was destroyed by English invaders in 1385 (the only substantial remains are the central piers that support the tower). St Giles was at the heart of the Scottish Reformation, and John Knox served as minister here from 1559 to 1572.
There are several ornate monuments in the church, including the tombs of James Graham, Marquis of Montrose, who led Charles I's forces in Scotland and was hanged in 1650 at the Mercat Cross; and his Covenanter opponent Archibald Campbell, Marquis of Argyll, who was decapitated in 1661 after the Restoration of Charles II. There's also a bronze memorial to author Robert Louis Stevenson, and a copy of the National Covenant of 1638.
By the side of the street, outside the western door of St Giles, is the Heart of Midlothian, set into the cobblestone paving. This marks the site of the Tolbooth. Built in the 15th century and demolished in the early 19th century, the Tolbooth served variously as a meeting place for parliament, the town council and the General Assembly of the Reformed Kirk, before becoming law courts and, finally, a notorious prison and place of execution. Passers-by traditionally spit on the heart for luck (don't stand downwind!).
At the other end of St Giles is the Mercat Cross, a 19th-century copy of the 1365 original, where merchants and traders met to transact business and royal proclamations were read.