output a referencing field in node tpl In a node type hotel I have an entity reference field to a node type offer. For the offer node.tpl I need to output some fields of the referencing node type hotel.

I have no idea how to get these fields inside the referenced node.
I'd put this in a comment but have no rep so I can't ...

Create a view of hotels as Robin said. The entity reference module provides views relationships that go in both directions , so add a relationship that corresponds to "entity referenced from field yadda yadda" -- sorry I don't know exactly how it'll be labeled offhand but with some trial and error you should be able to find the right one. 

Add a contextual filter using the offer relationship on nid, default to content id from url. Be sure to choose the offer relationship when adding fields.

To attach the view to the node itself, you can either use Viewfield or just embed it directly in the template (or preprocess function) using views_embed_view (link)