  We present optical integral field observations of the H II region containing
the ultraluminous X-ray source Holmberg II X-1. We confirm the existence of an
X-ray ionized nebula as the counterpart of the source due to the detection of
an extended He II (4686A) region (21 x 47 pc) at the Chandra ACIS-S position.
An extended blue objects with a size of 11 x 14 pc is coincident with the
X-ray/He II region, which could indicate either a young stellar complex or a
cluster. We have derived an X-ray to optical luminosity ratio of Lx/Lb>170, and
presumable it is Lx/Lb~300-400 using the recent HST ACS data. We find a complex
velocity dispersion at the position of the ULX. In addition, there is a radial
velocity variation in the X-ray ionized region found in the He II emission of
+-50 km/s on spatial scales of 2-3 arcsec. We believe that the putative black
hole not only ionizes the surrounding HII gas, but also perturbs it dynamically
(via jets or the accretion disk wind). The spatial analysis of the public
Chandra ACIS-S data reveals a point-like X-ray source and marginal indication
of an extended component (<<15 % of the total flux). The XMM-Newton EPIC-PN
spectrum of HoII X-1 is best fitted with an absorbed power-law in addition to
either a thermal thick plasma or a thermal thin plasma or a multi-colour disk
black body (MCD). In all cases, the thermal component shows relatively low
temperatures (kT~0.14-0.22 keV). Finally we discuss the optical/X-ray
properties of HoII X-1 with regards to the possible nature of the source.
