  Galactic supernova remnants (SNRs) with angular dimensions greater than a few
degrees are relatively rare, as are remnants located more than ten degrees off
the Galactic plane. Here we report a UV and optical investigation of two
previously suspected SNRs more than ten degrees in both angular diameter and
Galactic latitude. One is a proposed remnant discovered in 2008 through 1420
MHz polarization maps near Galactic coordinates $l$ = 353, $b$ = $-$34. GALEX
far UV (FUV) and H$\alpha$ emission mosaics show the object's radio emission
coincident with a 11 x 14 degree shell of UV filaments surrounding a diffuse
H$\alpha$ emission ring. Another proposed high latitude SNR is the 20 x 26
degree Antlia nebula (G275.5+18.4) discovered in 2002 through low-resolution
all-sky H$\alpha$ and ROSAT soft X-ray emissions. GALEX UV and H$\alpha$
mosaics along with optical spectra indicate the presence of shocks throughout
the Antlia nebula with estimated shock velocities of 70 to over 100 km
s$^{-1}$. We also present evidence that it has collided with the northeast rim
of the Gum Nebula. We find both of these nebulae are bona fide SNRs with ages
less than 10$^{5}$ yr despite their unusually large angular dimensions. We also
present FUV and optical images along with optical spectra of a new
high-latitude SNR (G249.7+24.7) some 4.5 degrees in diameter which has also
been independently discovered in X-rays and radio (Becker at al. 2021). We find
this remnant's distance to be $\leq$400 pc based on the detection of red and
blue shifted Na I absorption features in the spectra of two background stars.
