The Hogwarts kitchens are situated exactly beneath the Great Hall, with four wooden tables matching the tables above. It is a huge, high-ceilinged room, with a stone-flagged floor, pots and pans on the stone walls, and a great brick fireplace (GF21, GF28).
The school kitchens are accessable by going through a door in the entrance hall and taking the stairs downwards. Downstairs, in a broad stone basement corridor, brightly lit and decorated with food-themed paintings, one can tickle a pear on a painting of a bowl of fruit. The pear will giggle and turn into a large green door handel, revealing the entrance to the Hogwarts kitchens (GF21).
Harry visited the kitchen for the first time in his fourth year, after Hermione had found out about the entrance to the kitchen from Fred and George (GF21). Fred, George and Harry's father used to steal food from the kitchens (PS13, PS17). After completing his second task, Harry went down to the kitchens to present Dobby with new socks (GF28).
Over a hundred house-elves worked in the Hogwarts's kitchens, including Dobby, Winky and - upon Harry's orders - Kreacher (GF21, HBP3). In the final battle with Voldemort, Kreacher led the house-elves into the fight from the kitchens (DH36).
Harry mentions once (PS12) that there is a suit of armor near the kitchens, which is before he finds out how to get there in his fourth year!
The Hogwarts's kitchens are mostly referred to in plural, whereas the homes mentioned have a singular kitchen.
A convenient setup allows the house-elves arrange the tables and serve the food without being seen by those they serve. -BB
Notice also that this arrangement puts the house-elves literally below the wizards and witches they serve. -BB