1RXS J180408.9–342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present $NuSTAR$, $Swift$, and $Chandra$ observations obtained around the peak brightness of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of $LX$ $\simeq$ (2–3) × 10$\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$($D$/5.8 kpc)$2$ erg s$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ (0.5–10 keV). The $NuSTAR$ data reveal a broad Fe–K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disc is viewed at an inclination of $i$ $\simeq$ 27$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}$–35$\mathrm{<mrow\; data-mjx-texclass="ORD">\circ </mrow>}$ and extended close to the neutron star, down to $Rin$ $\simeq$ 5–7.5 gravitational radii ($\simeq$11–17 km). This inner disc radius suggests that the neutron star magnetic field strength is $B$ $\lesssim$ 2 × 10$8$ G. We find a narrow absorption line in the $Chandra$/HEG data at an energy of $\simeq$7.64 keV with a significance of $\simeq$4.8$\sigma$. This feature could correspond to blueshifted Fe $XXVI$ and arise from an accretion disc wind, which would imply an outflow velocity of $vout$ $\simeq$0.086$c$ ($\simeq$25800kms$^{−1}$).However,thiswouldbeextremeforanX-raybinaryanditisunclearifadiscwindshouldbevisibleatthelowinclinationanglethatweinferfromourreflectionanalysis.Finally,wediscusshowtheX-rayandopticalpropertiesof1RXSJ180408.9–342058areconsistentwitharelativelysmall($P_\text{orb}$ $\lesssim$ 3 h) binary orbit.