Apparatus (20) is provided for use in a gastrointestinal tract (40) of a patient, including an inflatable device (22) configured to be moved through the gastrointestinal tract (40) to a treatment site in response to a difference between fluid pressure proximal to the inflatable device (22) and fluid pressure distal to the inflatable device (22). An optical system (24) coupled to the inflatable device (22) configured to image the gastrointestinal tract (40). A working channel (32) coupled to the inflatable device (22) and shaped to define a channel lumen therein to provide access from outside of the patient to the treatment site. A tool (34) configured to be passed through the channel lumen and to emerge from a distal end of the working channel (32). The tool (34) comprises a tool steering mechanism (44) to facilitate steering of the tool (34) from outside of the patient. Other embodiments are also described.