A turbine airfoil (150, 176, 200), comprising: a body having an airfoil wall; said body further comprising a base and tip disposed opposite the base, and a pressure sidewall (152,178) and suction sidewall (154,180) extending between a leading edge (212,156) and a trailing edge; a coolant chamber within the body; and a plurality of cooling passages within the airfoil wall, each cooling passage including: a first portion extending from a first point on an exterior surface of the airfoil wall to the coolant chamber, a second portion extending from a second point on the exterior surface of the airfoil wall distal from the first point to intersect a mid-portion of the first portion, and a cap element closing the first portion at the first point but leaving the second portion open, wherein each cooling passage has a single inlet in fluid communication with the coolant chamber and a single outlet at the second point of the second portion; and characterised in that the cap element includes a metal plug in the first portion at or near the first point, and further comprising a thermal barrier coating covering the exterior surface of the airfoil wall, the second portion of each cooling passage extending through the TBC at the second point thereof. a body having an airfoil wall; said body further comprising a base and tip disposed opposite the base, and a pressure sidewall (152,178) and suction sidewall (154,180) extending between a leading edge (212,156) and a trailing edge; a coolant chamber within the body; and a plurality of cooling passages within the airfoil wall, each cooling passage including: a first portion extending from a first point on an exterior surface of the airfoil wall to the coolant chamber, a second portion extending from a second point on the exterior surface of the airfoil wall distal from the first point to intersect a mid-portion of the first portion, and a cap element closing the first portion at the first point but leaving the second portion open, wherein each cooling passage has a single inlet in fluid communication with the coolant chamber and a single outlet at the second point of the second portion; and characterised in that the cap element includes a metal plug in the first portion at or near the first point, and further comprising a thermal barrier coating covering the exterior surface of the airfoil wall, the second portion of each cooling passage extending through the TBC at the second point thereof. a first portion extending from a first point on an exterior surface of the airfoil wall to the coolant chamber, a second portion extending from a second point on the exterior surface of the airfoil wall distal from the first point to intersect a mid-portion of the first portion, and a cap element closing the first portion at the first point but leaving the second portion open, wherein each cooling passage has a single inlet in fluid communication with the coolant chamber and a single outlet at the second point of the second portion; and characterised in that the cap element includes a metal plug in the first portion at or near the first point, and further comprising a thermal barrier coating covering the exterior surface of the airfoil wall, the second portion of each cooling passage extending through the TBC at the second point thereof.