You should contact your employer, explain your situation (in particular that you feel disadvantaged by not having a space to de-stress in) and ask whether you can visit a nearby café. As long as doing so would not be particularly disruptive or impractical, your employer should allow you to do this.
It may be a good idea to agree any variations to your adjustments with your employer in advance. For example, for health and safety reasons, they may need to know if you will be off site at a café, instead of on the premises.
* See also our blog: Mahlia describes taking time-out in her car.