...I'd get to London to see Thomas Demand's photographs of painstakingly constructed environments at the Serpentine Gallery. The show runs to August 20th and is open Monday through Sunday 10-6.
...I'd get to Birmingham to see Marcel Dzama's latest drawings, paintings, videos, and bear costume at the Ikon Gallery. Be quick, though, as the show comes down July 16. Ikon is open Tuesday through Sunday 11-6.
You can catch both shows in one day as London and Birmingham are located just a short (1hr. 30 min.) train ride apart.