Turbo trainer
A-road with no lights and few junctions.
Loop around the lanes, left turns preferred but my best one has several rights.
Loop including a big hill
Not any particular one, mix them up a bit- training is boring otherwise. Plus your body somehow figures out you are trying to train it and it starts playing up.
If you have a 'cross bike try doing your intervals on a grass circuit in the park or something.
If you can't face another interval session do a hilly ride instead. Or a regular ride, but throw in some hard efforts wherever the terrain best allows you to.
Intersperse anything that you call training with easy rides.