From an article at Ekathimerini.com (here):
Additional photos and information are available from the Ministry of Culture and Sports, which offers the following description:
The school of Aristotle, the Lykeion (Lyceum) (335 B.C.), one of the three oldest gymnasia in the city together with those of the Academy and Kynosarges, was situated on the outskirts of ancient Athens, outside the walls and the Gate of Diochares. As attested by ancient authors (Plutarch, Strabo, Pausanias), the Lykeion was a very extensive, verdant area between two rivers, the Eridanos to the north and the Illisos to the south, and beside the sanctuary of Lykeion (Lycian) Apollo and Herakles Pankrates. Athenian hoplites and ephebes, fulfilling their military duties, exercised in this idyllic area with its abundant waters.For some inspiring recent comments on the lasting significance of Aristotle's school, see the recent Valedictory address by Professor David Sedley "Godlikeness" (link available at kenodoxia). The entire talk is brilliant and should be listened to; the discussion of Aristotle's school begins around 49:00.
Regarding the reported date 335BC for the founding the "Lyceum" as a school, one should keep in mind the skepticism, based on sifting the relevant literary evidence, of Ingmar Düring:
Aristotle and Theophrastus and the circle of scholars and students around them met and lectured in the Lyceum, a public gymnasium open to everybody, since long ago well known as a place where foreign sophists and teachers gave lectures. As the years passed the circle of collaborators and students probably became more closely united, but the Peripatos as a school in the same sense as the Academy was not established until after Aristotle's death. (Aristotle in the Ancient Biographical Tradition, Göteborg 1957, p.461)