Near the modern town of Skala Oropou, the ancient Sanctuary of Amphiaraos, more commonly known as the Amphiaraion, can be reached by heading 6.5 km SE, roughly up the Mavrodhilisi ravine. 
 

The Modern Site
    The guard booth, right alongside the road, has just been rebuilt and they were in the process of building brand new bathrooms here.  Still the site is very isolated. Make sure you have brought your snacks and water with you.  There is supposedly a very good guide book recommended for this site and sold at the guard booth. I can't remember the exact name, but if you look at them you can probably spot it. It's a little more expensive but written by some noteworthy scholars.  There is also a small museum here, but it's been closed for decades. You can still walk around the lower side of it and take a look at a number of more delicate architectural members that are under a portico.  There are tons of ancient rooftiles all around so watch where you step.

    Though we did not go down to modern Oropos, usually known as Skala Oropos, there are a few hotels and tavernas there.  It a few kilometers away from the water's edge on the Straight of Euboea and in antiquity it was used as the nearest point of access for ships going across to Euboea.
    I would also like to thank Ann Blasingham for her explanations and tour of this site as well as for the bibliographies below.

Epigraphical Evidence:
    IG VII 235-503,     SEG XXVI 601-610,     SEG XXX 473,     SEG XXXI 415-492,     SEG XXXIII 404,     SEG XXXVI 442

    Fossey, J.M. Topography and Population of Ancient Boeiotia, vol I. Chicago, 1988.  Pp. 29-33 (includes list of inscriptions concerning the city of Oropos), pp. 36-37 (includes bibliography on the Amphiareion). (Buy it now!)
    Oikonomides, Al. N. "Inscriptions from Oropos and the Amphiareion." Horos 3 (1985), 19-23.
    Petrakos, Basileios.  Ho Oropos kai to hieron tou Amphiaraou.  Athens, 1968.  Covers epigraphical evidence for the city of Oropos and the Sanctuary of Amphiaraos; very good epigraphical bibliography for these sites through the early 1960's.
    --, Epigraphika tou Oropou. Athens, 1980.
    --, "He Epigraphika tou Oropou kai tou Ramnountos." Praktika tou He Diethnous Sunedriou Hellenikes kai Latinikes Epigrahikes (Athens, 1982).  Athens, 1984, pp.309-326, 337.  Includes additional bibliography.

Archaeological Evidence:
    Coulton, J.J. "The Stoa at the Amphiaraion, Oropos." BSA 63 (1968), 147-183.
    Fossey, J.M. (see epigraphical evidence)
    Lohr, Christoph. "Die Statuenbasen im Amphiareion von Oropos." AthMitt 108 (1993), 183-212.
    Petrakios, Basileios. "To Amphiareio tou Oropou." Archailogia 39 (1991), pp. 21-33. (No bibliography, but up-to-date description of current and prior work at the site.)
    --, The Amphiareion of Oropos. Athens, 1995. (Guidebook; site history and description in English, but no bibliography.)
    Travlos, John. Bildlexikon zur Topographie des antiken Attika. Tubingen, 1988. (Bibliography through early 1980's.)
    Glazer, Franz. "Die Klepsydra im Amphiareion bei Oropos." Pro Arte Antiqua. Festschrift fur Hedwig Kenner, vol. I. Vienna: A.F. Koska, 1982. pp. 130-136. (on the water clock)

Links:

• Hellenic Ministry of Culture - Amphiarion : Up to date information about the site's hours and admission prices as well as telephone numbers (no pics).
• Perseus Site : Amphiarion : Six seperate buildings are catalouged here. A good deal of information and a number of specific pictures.