Another famous landmark of L’ Ilot Sacré for sure is the world-wide-well- known “friture” to savour the real “Mussels from Brussels”, as opposed to the now mature (grin) “Muscles from Brussels”, aka Jean-Claude Van Dam. (Used to be a former Hollywood B-movie star of Belgian origin).
Adding a little historical gossip: It was said that Van Dam always hated that nickname, for the obvious mussel reasons about his abs and other mussels/muscles. I doubt if he ever ate at Chez Léon.
– “Chez Léon” -. 
This is the original moules-frites restaurant of Brussels. Management is still in the hands of the founding family (since 1893). Not to be compared to the franchised ones in other places in Belgium, France, the Middle East etc. The “Leon de Bruxelles” chain was originally started by the family but later sold to international investors. Quality is different and adapted to local taste. As for the original restaurant: very good quality but the service may vary, depending on the number of patrons. It tends sometimes to look like a food factory. My advice: visit outside the holiday season and avoid week-ends.
Their signature plate: 
And for starters, I ‘ll suggest the traditional “Tomate Crevettes”. Grey North sea shrimps with butter lettuce, tomato and home made mayonnaise: 
Below their promotional video that will make you hungry:
Btw, avoid the Italian or Portuguese places in this part of Brussels. There are very good Italian, Spanish and mediterranean restaurants in other parts of town, just not here.
About the addresses and info for the places I suggested: click the pic below and then click Restaurants in the upper red menu bar. It also provides an interactive link for Beer Shops and bars concentrated there – Courtesy “La Commune de l’ Ilot Sacré.”
Brussels Grande Place is of course a must-see; Manneke Pis and the less well-known Jeanneke Pis ( Pissing-Jeannie) are also worth a visit when you make a trip to Belgium’s and Europe’s Capital.
I ‘ll add 2 places not to miss in the area: Galeries St Hubert
and the already mentioned best restaurant of the Sacred Islet: “Aux Armes de Bruxelles”. Highly recommended, not cheap but really NOT a tourist trap. The mayor of Brussels is a frequent visitor. and that guy is the living definition of an Epicurean.
Foodies' Blog Atelier 