Passage 9.39.5
κατὰ δὲ τὸ μαντεῖον τοιάδε γίνεται. ἐπειδὰν ἀνδρὶ ἐς τοῦ Τροφωνίου κατιέναι δόξῃ, πρῶτα μὲν τεταγμένων ἡμερῶν δίαιταν ἐν οἰκήματι ἔχει, τὸ δὲ οἴκημα Δαίμονός τε ἀγαθοῦ καὶ Τύχης ἱερόν ἐστιν ἀγαθῆς· διαιτώμενος δὲ ἐνταῦθα τά τε ἄλλα καθαρεύει καὶ λουτρῶν εἴργεται θερμῶν, τὸ δὲ λουτρὸν ὁ ποταμός ἐστιν ἡ Ἕρκυνα· καί οἱ καὶ κρέα ἄφθονά ἐστιν ἀπὸ τῶν θυσιῶν, θύει γὰρ δὴ ὁ κατιὼν αὐτῷ τε τῷ Τροφωνίῳ καὶ τοῦ Τροφωνίου τοῖς παισί, πρὸς δὲ Ἀπόλλωνί τε καὶ Κρόνῳ καὶ Διὶ ἐπίκλησιν Βασιλεῖ καὶ Ἥρᾳ τε Ἡνιόχῃ καὶ Δήμητρι ἣν ἐπονομάζοντες Εὐρώπην τοῦ Τροφωνίου φασὶν εἶναι τροφόν.
The ritual performed at the oracle is as follows. When a man decides to descend to Trophonius, he first lives for a set number of days in a dedicated building. This building is sacred to the Good Spirit (Agathos Daimon) and Good Fortune (Agathe Tyche). While he stays there, he maintains ritual purity in various ways, abstaining from warm baths; his bath is instead the river Hercyna. He also has abundant meat from sacrifices, for the one descending offers sacrifices to Trophonius himself and to Trophonius' children, as well as to Apollo, Cronus, Zeus with the title “Basileus” (King), Hera called “Henioche” (Charioteer), and Demeter whom they surname Europa, claiming her to have been the nurse of Trophonius.