What is an example of “fundamental alteration” of the goods or services being offered?

The classic example which may or may not have really happened is for someone who is Deaf to ask that the lights in a planetarium be raised so that she could see her interpreter.  Of course, this would fundamentally alter the experience for everyone, including the person who asked.  However, even though the planetarium could - and probably did - deny this request, the planetarium still has obligations under the ADA.  One possible solution would be to offer the patron a seat off on the far right or left and position the interpreter with a dim light right in front of her.  Another would be to provide her with the narrator’s script and a clip on light.