A valve body in a passage of a housing connected to a through hole in a sealed machine casing can allow an inspection apparatus into an interior of the casing when open, and prevents fluid flow through the passage when closed. Seals can engage the inspection apparatus to prevent fluid flow through the passage during inspection or inspection apparatus movement. A guide conduit in the casing can include branches and can guide the inspection apparatus to multiple inspection sites. Guide marks can identify the branches to assist with navigation within the casing.