Oltářík, Castle ruin in Děkovka, Czech Republic

Oltářík is a castle ruin on the isolated tefrite hill Hrádek in the České středohoří, above Děkovka. Only the gate and a residential tower survive; other structures were of wood or dry-laid stone and are visible as terrain traces and small masonry remnants.

Jakoubek z Vřesovic, a Hussite captain, probably built the castle between 1434 and 1438 to secure his estates during a dispute with the Žatec–Loun league. The first written record dates from 1450, when he pledged it to Jan of Polensko for 300 kopecks of groschen. It was described as deserted in 1544 and last mentioned as a ruin in 1612.

The name Oltářík likely derives from the rock's altar-like shape, a diminutive of oltář (altar), though some scholars link it to biblical naming traditions. The castle's name faded from memory after 1612 and was only reattached to the site by František Alexandr Heber in the 19th century.

The best route starts from Děkovka on marked trails leading up the hill, a walk of about ten minutes that is easy to follow. Visitors should wear sturdy shoes as the ground is uneven and sometimes slippery in places.

The name Oltářík was forgotten after the castle's last mention in 1612 and only reattached to the site by František Alexandr Heber in the 19th century. Some researchers link the name to biblical place names like Sion or Kalich, while Ivan Lehký and Milan Sýkora argue the rock itself resembles an altar, with the diminutive reflecting the castle's small size.