This Maas romanesque church can be considered as a fine example for its time in this region (arround the river Maas) with a basilical nave.
On the west side stands a closed western block or western tower, with on both sides a round staircase tower. On the eastern side lies the choir, flanked on both sides by an apsis. Below the tower remains a 9th century crypt. In this crypt the relics of Saint Hadelinus are kept in a niche. A second crypt can be found underneath the choir.
The facades of the aisles and the low transept are decorated with clamp butresses.
The choir stalls date from the 13th century, and thus is the oldest of its kind in Belgium.
A nice (french) site about Saint Hadelins: http://www.celles.org/tag/saint-hadelin/